Merge remote-tracking branch 'upstream/main' into feature/scalar-quantized-off-heap-scoring

dev-tools/scripts/diff_lucene_changes.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+import re
+import subprocess
+import sys
+import tempfile
+import urllib.request
+
+'''
+A simple tool to see diffs between main's version of CHANGES.txt entries for
+a given release vs the stable branch's version.  It's best to keep these 1)
+identical and 2) matching what changes were actually backported to be honest
+to users and avoid future annoying conflicts on backport.
+'''
+
+# e.g. python3 -u diff_lucene_changes.py branch_9_9 main 9.9.0
+
+#
+
+def get_changes_url(branch_name):
+  if os.path.isdir(branch_name):
+    url = f'file://{branch_name}/lucene/CHANGES.txt'
+  else:
+    url = f'https://raw.githubusercontent.com/apache/lucene/{branch_name}/lucene/CHANGES.txt'
+  print(f'NOTE: resolving {branch_name} --> {url}')
+  return url
+
+def extract_release_section(changes_txt, release_name):
+  return re.search(f'=======+ Lucene {re.escape(release_name)} =======+(.*?)=======+ Lucene .*? =======+$',
+                   changes_txt.decode('utf-8'), re.MULTILINE | re.DOTALL).group(1).encode('utf-8')
+
+def main():
+  if len(sys.argv) < 3 or len(sys.argv) > 5:
+    print('\nUsage: python3 -u dev-tools/scripts/diff_lucene_changes.py <branch1-or-local-clone> <branch2-or-local-clone> <release-name> [diff-commandline-extras]\n')
+    print('  e.g.: python3 -u dev-tools/scripts/diff_lucene_changes.py branch_9_9 /l/trunk 9.9.0 "-w"\n')
+    sys.exit(1)
+
+  branch1 = sys.argv[1]
+  branch2 = sys.argv[2]
+  release_name = sys.argv[3]
+
+  if len(sys.argv) > 4:
+    diff_cl_extras = [sys.argv[4]]
+  else:
+    diff_cl_extras = []
+
+  branch1_changes = extract_release_section(urllib.request.urlopen(get_changes_url(branch1)).read(),
+                                            release_name)
+  branch2_changes = extract_release_section(urllib.request.urlopen(get_changes_url(branch2)).read(),
+                                            release_name)
+
+  with tempfile.NamedTemporaryFile() as f1, tempfile.NamedTemporaryFile() as f2:
+    f1.write(branch1_changes)
+    f2.write(branch2_changes)
+
+    command = ['diff'] + diff_cl_extras + [f1.name, f2.name]
+
+    # diff returns non-zero exit status when there are diffs, so don't pass check=True
+    print(subprocess.run(command, check=False, capture_output=True).stdout.decode('utf-8'))
+
+if __name__ == '__main__':
+  main()

gradle/generation/forUtil.gradle

@@ -23,7 +23,7 @@ configure(project(":lucene:core")) {
     description "Regenerate gen_ForUtil.py"
     group "generation"
 
-    def genDir = file("src/java/org/apache/lucene/codecs/lucene99")
+    def genDir = file("src/java/org/apache/lucene/codecs/lucene912")
     def genScript = file("${genDir}/gen_ForUtil.py")
     def genOutput = file("${genDir}/ForUtil.java")
 
@@ -96,5 +96,30 @@ configure(project(":lucene:backward-codecs")) {
           andThenTasks: ["spotlessJava", "spotlessJavaApply"],
           mustRunBefore: [ "compileJava" ]
   ])
+
+  task generateForUtil99Internal() {
+    description "Regenerate gen_ForUtil.py"
+    group "generation"
+
+    def genDir = file("src/java/org/apache/lucene/backward_codecs/lucene99")
+    def genScript = file("${genDir}/gen_ForUtil.py")
+    def genOutput = file("${genDir}/ForUtil.java")
+
+    inputs.file genScript
+    outputs.file genOutput
+
+    doLast {
+      quietExec {
+        workingDir genDir
+        executable project.externalTool("python3")
+        args = [ '-B', genScript ]
+      }
+    }
+  }
+
+  regenerate.dependsOn wrapWithPersistentChecksums(generateForUtil99Internal, [
+          andThenTasks: ["spotlessJava", "spotlessJavaApply"],
+          mustRunBefore: [ "compileJava" ]
+  ])
 }
 

lucene/CHANGES.txt

@@ -80,10 +80,6 @@ API Changes
 * GITHUB#12875: Ensure token position is always increased in PathHierarchyTokenizer and ReversePathHierarchyTokenizer
   and resulting tokens do not overlap. (Michael Froh, Lukáš Vlček)
 
-* GITHUB#12624, GITHUB#12831: Allow FSTCompiler to stream to any DataOutput while building, and
-  make compile() only return the FSTMetadata. For on-heap (default) use case, please use
-  FST.fromFSTReader(fstMetadata, fstCompiler.getFSTReader()) to create the FST. (Anh Dung Bui)
-
 * GITHUB#13146, GITHUB#13148: Remove ByteBufferIndexInput and only use MemorySegment APIs
   for MMapDirectory.  (Uwe Schindler)
 
@@ -112,6 +108,11 @@ API Changes
 
 * GITHUB#13410: Removed Scorer#getWeight (Sanjay Dutt, Adrien Grand)
 
+* GITHUB#13499: Remove deprecated TopScoreDocCollector + TopFieldCollector methods (#create, #createSharedManager) (Jakub Slowinski)
+
+* GITHUB#13632: CandidateMatcher public matching functions (Bryan Jacobowitz)
+
+
 New Features
 ---------------------
 
@@ -133,6 +134,13 @@ New Features
   DocValuesSkipper abstraction. A new flag is added to FieldType.java that configures whether
   to create a "skip index" for doc values. (Ignacio Vera)
 
+* GITHUB#13563: Add levels to doc values skip index. (Ignacio Vera)
+
+* GITHUB#13597: Align doc value skipper interval boundaries when an interval contains a constant
+  value. (Ignacio Vera)
+
+* GITHUB#13604: Add Kmeans clustering on vectors (Mayya Sharipova, Jim Ferenczi, Tom Veasey)
+
 Improvements
 ---------------------
 
@@ -243,24 +251,65 @@ Other
 
 * GITHUB#13332: Improve MissingDoclet linter to check records correctly. (Uwe Schindler)
 
+* GITHUB#13499: Remove usage of TopScoreDocCollector + TopFieldCollector deprecated methods (#create, #createSharedManager) (Jakub Slowinski)
+
 ======================== Lucene 9.12.0 =======================
 
 API Changes
 ---------------------
 
-* GITHUB#13281: Mark COSINE VectorSimilarityFunction as deprecated. (Pulkit Gupta)
+* GITHUB#13469: Expose FlatVectorsFormat as a first-class format; can be configured using a custom Codec. (Michael Sokolov)
 
-* GITHUB#13469: Expose FlatVectorsFormat as a first-class format; can be configured using a custom Codec. (Michael Sokolov) 
+* GITHUB#13612: Hunspell: add Suggester#proceedPastRep to avoid losing relevant suggestions. (Peter Gromov)
+
+* GITHUB#13603: Introduced `IndexSearcher#searchLeaf(LeafReaderContext, Weight, Collector)` protected method to
+  facilitate customizing per-leaf behavior of search without requiring to override
+  `search(LeafReaderContext[], Weight, Collector)` which requires overriding the entire loop across the leaves (Luca Cavanna)
+
+* GITHUB#13559: Add BitSet#nextSetBit(int, int) to get the index of the first set bit in range. (Egor Potemkin)
+
+* GITHUB#13568: Add DoubleValuesSource#toSortableLongDoubleValuesSource and
+  MultiDoubleValuesSource#toSortableMultiLongValuesSource methods. (Shradha Shankar)
+
+* GITHUB#13568: Add CollectorOwner class that wraps CollectorManager, and handles list of Collectors and results.
+  Add IndexSearcher#search method that takes CollectorOwner. (Egor Potemkin)
+
+* GITHUB#13568: Add DrillSideways#search method that supports any collector types for any drill-sideways dimensions
+  or drill-down. (Egor Potemkin)
 
 New Features
 ---------------------
-(No changes)
+
+* GITHUB#13430: Allow configuring the search concurrency via
+  TieredMergePolicy#setTargetSearchConcurrency. This in-turn instructs the
+  merge policy to try to have at least this number of segments on the highest
+  tier. (Adrien Grand, Carlos Delgado)
+
+* GITHUB#13517: Allow configuring the search concurrency on LogDocMergePolicy
+  and LogByteSizeMergePolicy via a new #setTargetConcurrency setter.
+  (Adrien Grand)
+
+* GITHUB#13568: Add sandbox facets module to compute facets while collecting. (Egor Potemkin, Shradha Shankar)
 
 Improvements
 ---------------------
 
 * GITHUB#13548: Refactor and javadoc update for KNN vector writer classes. (Patrick Zhai)
 
+* GITHUB#13562: Add Intervals.regexp and Intervals.range methods to produce  IntervalsSource
+  for regexp and range queries. (Mayya Sharipova)
+
+* GITHUB#13625: Remove BitSet#nextSetBit code duplication. (Greg Miller)
+
+* GITHUB#13285: Early terminate graph searches of AbstractVectorSimilarityQuery to follow timeout set from
+  IndexSearcher#setTimeout(QueryTimeout). (Kaival Parikh)
+  
+* GITHUB#13633: Add ability to read/write knn vector values to a MemoryIndex. (Ben Trent)
+
+* GITHUB#12627: patch HNSW graphs to improve reachability of all nodes from entry points
+
+* GITHUB#13201: Better cost estimation on MultiTermQuery over few terms. (Michael Froh)
+
 Optimizations
 ---------------------
 
@@ -282,6 +331,30 @@ Optimizations
 
 * GITHUB#13538: Slightly reduce heap usage for HNSW and scalar quantized vector writers. (Ben Trent)
 
+* GITHUB#12100: WordBreakSpellChecker.suggestWordBreaks now does a breadth first search, allowing it to return
+  better matches with fewer evaluations (hossman)
+
+* GITHUB#13582: Stop requiring MaxScoreBulkScorer's outer window from having at
+  least INNER_WINDOW_SIZE docs. (Adrien Grand)
+
+* GITHUB#13570, GITHUB#13574, GITHUB#13535: Avoid performance degradation with closing shared Arenas.
+  Closing many individual index files can potentially lead to a degradation in execution performance.
+  Index files are mmapped one-to-one with the JDK's foreign shared Arena. The JVM deoptimizes the top
+  few frames of all threads when closing a shared Arena (see JDK-8335480). We mitigate this situation
+  by 1) using a confined Arena where appropriate, and 2) grouping files from the same segment to a
+  single shared Arena. (Chris Hegarty, Michael Gibney, Uwe Schindler)
+
+* GITHUB#13585: Lucene912PostingsFormat, the new default postings format, now
+  only has 2 levels of skip data, which are inlined into postings instead of
+  being stored at the end of postings lists. This translates into better
+  performance for queries that need skipping such as conjunctions.
+  (Adrien Grand)
+
+* GITHUB#13581: OnHeapHnswGraph no longer allocates a lock for every graph node (Mike Sokolov)
+
+* GITHUB#13636: Optimizations to the decoding logic of blocks of postings.
+  (Adrien Grand, Uwe Schindler)
+
 Changes in runtime behavior
 ---------------------
 
@@ -302,6 +375,11 @@ Bug Fixes
 * GITHUB#13553: Correct RamUsageEstimate for scalar quantized knn vector formats so that raw vectors are correctly
   accounted for. (Ben Trent)
 
+* GITHUB#13615: Correct scalar quantization when used in conjunction with COSINE similarity. Vectors are normalized
+  before quantization to ensure the cosine similarity is correctly calculated. (Ben Trent)
+
+* GITHUB#13627: Fix race condition on flush for DWPT seqNo generation. (Ben Trent, Ao Li)
+
 Other
 --------------------
 (No changes)
@@ -531,6 +609,10 @@ API Changes
 
 * GITHUB#12854: Mark DrillSideways#createDrillDownFacetsCollector as @Deprecated. (Greg Miller)
 
+* GITHUB#12624, GITHUB#12831: Allow FSTCompiler to stream to any DataOutput while building, and
+  make compile() only return the FSTMetadata. For on-heap (default) use case, please use
+  FST.fromFSTReader(fstMetadata, fstCompiler.getFSTReader()) to create the FST. (Anh Dung Bui)
+
 New Features
 ---------------------
 * GITHUB#12679: Add support for similarity-based vector searches using [Byte|Float]VectorSimilarityQuery. Uses a new
@@ -538,6 +620,12 @@ New Features
   better-scoring nodes are available, or the best candidate is below a score of `traversalSimilarity` in the lowest
   level. (Aditya Prakash, Kaival Parikh)
 
+* GITHUB#12829: For indices newly created as of 9.10.0 onwards, IndexWriter preserves document blocks indexed via
+  IndexWriter#addDocuments or IndexWriter#updateDocuments also when index sorting is configured. Document blocks are
+  maintained alongside their parent documents during sort and merge. IndexWriterConfig accepts a parent field that is used
+  to maintain block orders if index sorting is used. Note, this is fully optional in Lucene 9.x while will be mandatory for
+  indices that use document blocks together with index sorting as of 10.0.0. (Simon Willnauer)
+
 * GITHUB#12336: Index additional data per facet label in the taxonomy. (Shai Erera, Egor Potemkin, Mike McCandless,
   Stefan Vodita)
 
@@ -629,7 +717,6 @@ Build
 
 Other
 ---------------------
-
 * GITHUB#11023: Removing some dead code in CheckIndex. (Jakub Slowinski)
 
 * GITHUB#11023: Removing @lucene.experimental tags in testXXX methods in CheckIndex. (Jakub Slowinski)

lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/ModifyingSuggester.java

@@ -31,6 +31,7 @@ class ModifyingSuggester {
   private final String misspelled;
   private final WordCase wordCase;
   private final FragmentChecker fragmentChecker;
+  private final boolean proceedPastRep;
   private final char[] tryChars;
   private final Hunspell speller;
 
@@ -39,13 +40,15 @@ class ModifyingSuggester {
       LinkedHashSet<Suggestion> result,
       String misspelled,
       WordCase wordCase,
-      FragmentChecker checker) {
+      FragmentChecker checker,
+      boolean proceedPastRep) {
     this.speller = speller;
     tryChars = speller.dictionary.tryChars.toCharArray();
     this.result = result;
     this.misspelled = misspelled;
     this.wordCase = wordCase;
     fragmentChecker = checker;
+    this.proceedPastRep = proceedPastRep;
   }
 
   /**
@@ -125,9 +128,9 @@ class ModifyingSuggester {
     boolean hasGoodSuggestions = trySuggestion(word.toUpperCase(Locale.ROOT));
 
     GradedSuggestions repResult = tryRep(word);
-    if (repResult == GradedSuggestions.Best) return true;
+    if (repResult == GradedSuggestions.Best && !proceedPastRep) return true;
 
-    hasGoodSuggestions |= repResult == GradedSuggestions.Normal;
+    hasGoodSuggestions |= repResult != GradedSuggestions.None;
 
     if (!speller.dictionary.mapTable.isEmpty()) {
       enumerateMapReplacements(word, "", 0);

lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/Suggester.java

@@ -53,16 +53,21 @@ public class Suggester {
   private final Dictionary dictionary;
   private final SuggestibleEntryCache suggestibleCache;
   private final FragmentChecker fragmentChecker;
+  private final boolean proceedPastRep;
 
   public Suggester(Dictionary dictionary) {
-    this(dictionary, null, FragmentChecker.EVERYTHING_POSSIBLE);
+    this(dictionary, null, FragmentChecker.EVERYTHING_POSSIBLE, false);
   }
 
   private Suggester(
-      Dictionary dictionary, SuggestibleEntryCache suggestibleCache, FragmentChecker checker) {
+      Dictionary dictionary,
+      SuggestibleEntryCache suggestibleCache,
+      FragmentChecker checker,
+      boolean proceedPastRep) {
     this.dictionary = dictionary;
     this.suggestibleCache = suggestibleCache;
     this.fragmentChecker = checker;
+    this.proceedPastRep = proceedPastRep;
   }
 
   /**
@@ -71,8 +76,8 @@ public class Suggester {
    * entries are stored as fast-to-iterate plain words instead of highly compressed prefix trees.
    */
   public Suggester withSuggestibleEntryCache() {
-    return new Suggester(
-        dictionary, SuggestibleEntryCache.buildCache(dictionary.words), fragmentChecker);
+    SuggestibleEntryCache cache = SuggestibleEntryCache.buildCache(dictionary.words);
+    return new Suggester(dictionary, cache, fragmentChecker, proceedPastRep);
   }
 
   /**
@@ -80,7 +85,17 @@ public class Suggester {
    * the performance of the "Modification" phase performance.
    */
   public Suggester withFragmentChecker(FragmentChecker checker) {
-    return new Suggester(dictionary, suggestibleCache, checker);
+    return new Suggester(dictionary, suggestibleCache, checker, proceedPastRep);
+  }
+
+  /**
+   * Returns a copy of this suggester instance that doesn't stop after encountering acceptable words
+   * after applying REP rules. By default, Hunspell stops when it finds any, but this behavior may
+   * not always be desirable, e.g., if we have "REP i ea", "tims" be replaced only by "teams" and
+   * not "times", which could also be meant.
+   */
+  public Suggester proceedPastRep() {
+    return new Suggester(dictionary, suggestibleCache, fragmentChecker, true);
   }
 
   /**
@@ -174,7 +189,8 @@ public class Suggester {
     }
 
     boolean hasGoodSuggestions =
-        new ModifyingSuggester(suggestionSpeller, suggestions, word, wordCase, fragmentChecker)
+        new ModifyingSuggester(
+                suggestionSpeller, suggestions, word, wordCase, fragmentChecker, proceedPastRep)
             .suggest();
 
     if (!hasGoodSuggestions && dictionary.maxNGramSuggestions > 0) {

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/TestSpellChecking.java

@@ -59,6 +59,14 @@ public class TestSpellChecking extends LuceneTestCase {
 
   public void testRepSuggestions() throws Exception {
     doTest("rep");
+
+    //noinspection DataFlowIssue
+    Path aff = Path.of(getClass().getResource("rep.aff").toURI());
+    Dictionary dictionary = TestAllDictionaries.loadDictionary(aff);
+    Suggester suggester = new Suggester(dictionary);
+    assertEquals(List.of("auto's"), suggester.suggestNoTimeout("autos", () -> {}));
+    assertEquals(
+        List.of("auto's", "auto"), suggester.proceedPastRep().suggestNoTimeout("autos", () -> {}));
   }
 
   public void testPhSuggestions() throws Exception {

lucene/backward-codecs/src/generated/checksums/generateForUtil99.json

@@ -0,0 +1,4 @@
+{
+    "lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/ForUtil.java": "f31797842f047626df6a1a6b97167bec60269fec",
+    "lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/gen_ForUtil.py": "325f2610974b0e76e278b6445405a098a3763feb"
+}

lucene/backward-codecs/src/java/module-info.java

@@ -35,6 +35,7 @@ module org.apache.lucene.backward_codecs {
   exports org.apache.lucene.backward_codecs.lucene92;
   exports org.apache.lucene.backward_codecs.lucene94;
   exports org.apache.lucene.backward_codecs.lucene95;
+  exports org.apache.lucene.backward_codecs.lucene99;
   exports org.apache.lucene.backward_codecs.packed;
   exports org.apache.lucene.backward_codecs.store;
 
@@ -43,7 +44,8 @@ module org.apache.lucene.backward_codecs {
   provides org.apache.lucene.codecs.PostingsFormat with
       org.apache.lucene.backward_codecs.lucene50.Lucene50PostingsFormat,
       org.apache.lucene.backward_codecs.lucene84.Lucene84PostingsFormat,
-      org.apache.lucene.backward_codecs.lucene90.Lucene90PostingsFormat;
+      org.apache.lucene.backward_codecs.lucene90.Lucene90PostingsFormat,
+      org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat;
   provides org.apache.lucene.codecs.KnnVectorsFormat with
       org.apache.lucene.backward_codecs.lucene90.Lucene90HnswVectorsFormat,
       org.apache.lucene.backward_codecs.lucene91.Lucene91HnswVectorsFormat,
@@ -59,5 +61,6 @@ module org.apache.lucene.backward_codecs {
       org.apache.lucene.backward_codecs.lucene91.Lucene91Codec,
       org.apache.lucene.backward_codecs.lucene92.Lucene92Codec,
       org.apache.lucene.backward_codecs.lucene94.Lucene94Codec,
-      org.apache.lucene.backward_codecs.lucene95.Lucene95Codec;
+      org.apache.lucene.backward_codecs.lucene95.Lucene95Codec,
+      org.apache.lucene.backward_codecs.lucene99.Lucene99Codec;
 }

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/ForDeltaUtil.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import org.apache.lucene.store.DataInput;

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/ForUtil.java

@@ -16,7 +16,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import org.apache.lucene.store.DataInput;

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/Lucene99Codec.java

@@ -14,12 +14,33 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.util.Objects;
-import org.apache.lucene.codecs.*;
-import org.apache.lucene.codecs.lucene90.*;
+import org.apache.lucene.codecs.Codec;
+import org.apache.lucene.codecs.CompoundFormat;
+import org.apache.lucene.codecs.DocValuesFormat;
+import org.apache.lucene.codecs.FieldInfosFormat;
+import org.apache.lucene.codecs.FilterCodec;
+import org.apache.lucene.codecs.KnnVectorsFormat;
+import org.apache.lucene.codecs.LiveDocsFormat;
+import org.apache.lucene.codecs.NormsFormat;
+import org.apache.lucene.codecs.PointsFormat;
+import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.SegmentInfoFormat;
+import org.apache.lucene.codecs.StoredFieldsFormat;
+import org.apache.lucene.codecs.TermVectorsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90CompoundFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90NormsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90PointsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat;
 import org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat;
+import org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat;
+import org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat;
 import org.apache.lucene.codecs.perfield.PerFieldDocValuesFormat;
 import org.apache.lucene.codecs.perfield.PerFieldKnnVectorsFormat;
 import org.apache.lucene.codecs.perfield.PerFieldPostingsFormat;
@@ -98,7 +119,7 @@ public class Lucene99Codec extends Codec {
     super("Lucene99");
     this.storedFieldsFormat =
         new Lucene90StoredFieldsFormat(Objects.requireNonNull(mode).storedMode);
-    this.defaultPostingsFormat = new Lucene99PostingsFormat();
+    this.defaultPostingsFormat = new Lucene912PostingsFormat();
     this.defaultDVFormat = new Lucene90DocValuesFormat();
     this.defaultKnnVectorsFormat = new Lucene99HnswVectorsFormat();
   }

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/Lucene99PostingsFormat.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import org.apache.lucene.codecs.BlockTermState;
@@ -24,7 +24,6 @@ import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.MultiLevelSkipListWriter;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.PostingsReaderBase;
-import org.apache.lucene.codecs.PostingsWriterBase;
 import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsReader;
 import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
 import org.apache.lucene.index.IndexOptions;
@@ -339,7 +338,7 @@ import org.apache.lucene.util.packed.PackedInts;
  *
  * @lucene.experimental
  */
-public final class Lucene99PostingsFormat extends PostingsFormat {
+public class Lucene99PostingsFormat extends PostingsFormat {
 
   /**
    * Filename extension for document number, frequencies, and skip data. See chapter: <a
@@ -374,28 +373,9 @@ public final class Lucene99PostingsFormat extends PostingsFormat {
   static final int VERSION_START = 0;
   static final int VERSION_CURRENT = VERSION_START;
 
-  private final int minTermBlockSize;
-  private final int maxTermBlockSize;
-
   /** Creates {@code Lucene99PostingsFormat} with default settings. */
   public Lucene99PostingsFormat() {
-    this(
-        Lucene90BlockTreeTermsWriter.DEFAULT_MIN_BLOCK_SIZE,
-        Lucene90BlockTreeTermsWriter.DEFAULT_MAX_BLOCK_SIZE);
-  }
-
-  /**
-   * Creates {@code Lucene99PostingsFormat} with custom values for {@code minBlockSize} and {@code
-   * maxBlockSize} passed to block terms dictionary.
-   *
-   * @see
-   *     Lucene90BlockTreeTermsWriter#Lucene90BlockTreeTermsWriter(SegmentWriteState,PostingsWriterBase,int,int)
-   */
-  public Lucene99PostingsFormat(int minTermBlockSize, int maxTermBlockSize) {
     super("Lucene99");
-    Lucene90BlockTreeTermsWriter.validateSettings(minTermBlockSize, maxTermBlockSize);
-    this.minTermBlockSize = minTermBlockSize;
-    this.maxTermBlockSize = maxTermBlockSize;
   }
 
   @Override
@@ -405,19 +385,7 @@ public final class Lucene99PostingsFormat extends PostingsFormat {
 
   @Override
   public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
-    PostingsWriterBase postingsWriter = new Lucene99PostingsWriter(state);
-    boolean success = false;
-    try {
-      FieldsConsumer ret =
-          new Lucene90BlockTreeTermsWriter(
-              state, postingsWriter, minTermBlockSize, maxTermBlockSize);
-      success = true;
-      return ret;
-    } finally {
-      if (!success) {
-        IOUtils.closeWhileHandlingException(postingsWriter);
-      }
-    }
+    throw new UnsupportedOperationException();
   }
 
   @Override

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/Lucene99PostingsReader.java

@@ -14,23 +14,23 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
-import static org.apache.lucene.codecs.lucene99.ForUtil.BLOCK_SIZE;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.DOC_CODEC;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.MAX_SKIP_LEVELS;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.PAY_CODEC;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.POS_CODEC;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.TERMS_CODEC;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.VERSION_CURRENT;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.VERSION_START;
+import static org.apache.lucene.backward_codecs.lucene99.ForUtil.BLOCK_SIZE;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.DOC_CODEC;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.MAX_SKIP_LEVELS;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.PAY_CODEC;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.POS_CODEC;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.TERMS_CODEC;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.VERSION_CURRENT;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.VERSION_START;
 
 import java.io.IOException;
 import java.util.Arrays;
+import org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.IntBlockTermState;
 import org.apache.lucene.codecs.BlockTermState;
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.codecs.PostingsReaderBase;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.IntBlockTermState;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.Impacts;
 import org.apache.lucene.index.ImpactsEnum;

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/Lucene99ScoreSkipReader.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import java.util.AbstractList;

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/Lucene99SkipReader.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import java.util.Arrays;
@@ -61,6 +61,7 @@ public class Lucene99SkipReader extends MultiLevelSkipListReader {
   private long lastDocPointer;
   private int lastPosBufferUpto;
 
+  /** Sole constructor. */
   public Lucene99SkipReader(
       IndexInput skipStream,
       int maxSkipLevels,
@@ -98,6 +99,7 @@ public class Lucene99SkipReader extends MultiLevelSkipListReader {
     return df % ForUtil.BLOCK_SIZE == 0 ? df - 1 : df;
   }
 
+  /** Initialize state. */
   public void init(
       long skipPointer, long docBasePointer, long posBasePointer, long payBasePointer, int df)
       throws IOException {
@@ -125,22 +127,27 @@ public class Lucene99SkipReader extends MultiLevelSkipListReader {
     return lastDocPointer;
   }
 
+  /** Returns the pointer in the pos file. */
   public long getPosPointer() {
     return lastPosPointer;
   }
 
+  /** Return the start offset in the position block. */
   public int getPosBufferUpto() {
     return lastPosBufferUpto;
   }
 
+  /** Returns the pointer in the pay file. */
   public long getPayPointer() {
     return lastPayPointer;
   }
 
+  /** Return the number of bytes in the pay block that belongs to docs from the previous block. */
   public int getPayloadByteUpto() {
     return lastPayloadByteUpto;
   }
 
+  /** Return the next skip doc, no skipping can be performed until this doc. */
   public int getNextSkipDoc() {
     return skipDoc[0];
   }
@@ -199,7 +206,7 @@ public class Lucene99SkipReader extends MultiLevelSkipListReader {
     return delta;
   }
 
-  // The default impl skips impacts
+  /** Read impacts. The default implementation skips them. */
   protected void readImpacts(int level, IndexInput skipStream) throws IOException {
     skipStream.skipBytes(skipStream.readVInt());
   }

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/Lucene99SkipWriter.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import java.util.Arrays;
@@ -46,10 +46,10 @@ import org.apache.lucene.store.IndexOutput;
  * uptos(position, payload). 4. start offset.
  */
 public final class Lucene99SkipWriter extends MultiLevelSkipListWriter {
-  private int[] lastSkipDoc;
-  private long[] lastSkipDocPointer;
-  private long[] lastSkipPosPointer;
-  private long[] lastSkipPayPointer;
+  private final int[] lastSkipDoc;
+  private final long[] lastSkipDocPointer;
+  private final long[] lastSkipPosPointer;
+  private final long[] lastSkipPayPointer;
 
   private final IndexOutput docOut;
   private final IndexOutput posOut;
@@ -61,11 +61,12 @@ public final class Lucene99SkipWriter extends MultiLevelSkipListWriter {
   private long curPayPointer;
   private int curPosBufferUpto;
   private int curPayloadByteUpto;
-  private CompetitiveImpactAccumulator[] curCompetitiveFreqNorms;
+  private final CompetitiveImpactAccumulator[] curCompetitiveFreqNorms;
   private boolean fieldHasPositions;
   private boolean fieldHasOffsets;
   private boolean fieldHasPayloads;
 
+  /** Sole constructor. */
   public Lucene99SkipWriter(
       int maxSkipLevels,
       int blockSize,
@@ -84,7 +85,12 @@ public final class Lucene99SkipWriter extends MultiLevelSkipListWriter {
       lastSkipPosPointer = new long[maxSkipLevels];
       if (payOut != null) {
         lastSkipPayPointer = new long[maxSkipLevels];
+      } else {
+        lastSkipPayPointer = null;
       }
+    } else {
+      lastSkipPosPointer = null;
+      lastSkipPayPointer = null;
     }
     curCompetitiveFreqNorms = new CompetitiveImpactAccumulator[maxSkipLevels];
     for (int i = 0; i < maxSkipLevels; ++i) {
@@ -92,6 +98,7 @@ public final class Lucene99SkipWriter extends MultiLevelSkipListWriter {
     }
   }
 
+  /** Reset state for the given index options. */
   public void setField(
       boolean fieldHasPositions, boolean fieldHasOffsets, boolean fieldHasPayloads) {
     this.fieldHasPositions = fieldHasPositions;
@@ -211,6 +218,7 @@ public final class Lucene99SkipWriter extends MultiLevelSkipListWriter {
     competitiveFreqNorms.clear();
   }
 
+  /** Write impacts to the given output. */
   public static void writeImpacts(CompetitiveImpactAccumulator acc, DataOutput out)
       throws IOException {
     Collection<Impact> impacts = acc.getCompetitiveFreqNormPairs();

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/PForUtil.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import java.util.Arrays;

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/PostingsUtil.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import org.apache.lucene.store.IndexInput;

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/gen_ForUtil.py

@@ -40,7 +40,7 @@ HEADER = """// This file has been automatically generated, DO NOT EDIT
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import java.io.IOException;
 import org.apache.lucene.store.DataInput;

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene99/package-info.java

@@ -0,0 +1,428 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Lucene 9.9 file format.
+ *
+ * <h2>Apache Lucene - Index File Formats</h2>
+ *
+ * <div>
+ *
+ * <ul>
+ *   <li><a href="#Introduction">Introduction</a>
+ *   <li><a href="#Definitions">Definitions</a>
+ *       <ul>
+ *         <li><a href="#Inverted_Indexing">Inverted Indexing</a>
+ *         <li><a href="#Types_of_Fields">Types of Fields</a>
+ *         <li><a href="#Segments">Segments</a>
+ *         <li><a href="#Document_Numbers">Document Numbers</a>
+ *       </ul>
+ *   <li><a href="#Overview">Index Structure Overview</a>
+ *   <li><a href="#File_Naming">File Naming</a>
+ *   <li><a href="#file-names">Summary of File Extensions</a>
+ *       <ul>
+ *         <li><a href="#Lock_File">Lock File</a>
+ *         <li><a href="#History">History</a>
+ *         <li><a href="#Limitations">Limitations</a>
+ *       </ul>
+ * </ul>
+ *
+ * </div> <a id="Introduction"></a>
+ *
+ * <h3>Introduction</h3>
+ *
+ * <div>
+ *
+ * <p>This document defines the index file formats used in this version of Lucene. If you are using
+ * a different version of Lucene, please consult the copy of <code>docs/</code> that was distributed
+ * with the version you are using.
+ *
+ * <p>This document attempts to provide a high-level definition of the Apache Lucene file formats.
+ * </div> <a id="Definitions"></a>
+ *
+ * <h3>Definitions</h3>
+ *
+ * <div>
+ *
+ * <p>The fundamental concepts in Lucene are index, document, field and term.
+ *
+ * <p>An index contains a sequence of documents.
+ *
+ * <ul>
+ *   <li>A document is a sequence of fields.
+ *   <li>A field is a named sequence of terms.
+ *   <li>A term is a sequence of bytes.
+ * </ul>
+ *
+ * <p>The same sequence of bytes in two different fields is considered a different term. Thus terms
+ * are represented as a pair: the string naming the field, and the bytes within the field. <a
+ * id="Inverted_Indexing"></a>
+ *
+ * <h4>Inverted Indexing</h4>
+ *
+ * <p>Lucene's index stores terms and statistics about those terms in order to make term-based
+ * search more efficient. Lucene's terms index falls into the family of indexes known as an
+ * <i>inverted index.</i> This is because it can list, for a term, the documents that contain it.
+ * This is the inverse of the natural relationship, in which documents list terms. <a
+ * id="Types_of_Fields"></a>
+ *
+ * <h4>Types of Fields</h4>
+ *
+ * <p>In Lucene, fields may be <i>stored</i>, in which case their text is stored in the index
+ * literally, in a non-inverted manner. Fields that are inverted are called <i>indexed</i>. A field
+ * may be both stored and indexed.
+ *
+ * <p>The text of a field may be <i>tokenized</i> into terms to be indexed, or the text of a field
+ * may be used literally as a term to be indexed. Most fields are tokenized, but sometimes it is
+ * useful for certain identifier fields to be indexed literally.
+ *
+ * <p>See the {@link org.apache.lucene.document.Field Field} java docs for more information on
+ * Fields. <a id="Segments"></a>
+ *
+ * <h4>Segments</h4>
+ *
+ * <p>Lucene indexes may be composed of multiple sub-indexes, or <i>segments</i>. Each segment is a
+ * fully independent index, which could be searched separately. Indexes evolve by:
+ *
+ * <ol>
+ *   <li>Creating new segments for newly added documents.
+ *   <li>Merging existing segments.
+ * </ol>
+ *
+ * <p>Searches may involve multiple segments and/or multiple indexes, each index potentially
+ * composed of a set of segments. <a id="Document_Numbers"></a>
+ *
+ * <h4>Document Numbers</h4>
+ *
+ * <p>Internally, Lucene refers to documents by an integer <i>document number</i>. The first
+ * document added to an index is numbered zero, and each subsequent document added gets a number one
+ * greater than the previous.
+ *
+ * <p>Note that a document's number may change, so caution should be taken when storing these
+ * numbers outside of Lucene. In particular, numbers may change in the following situations:
+ *
+ * <ul>
+ *   <li>
+ *       <p>The numbers stored in each segment are unique only within the segment, and must be
+ *       converted before they can be used in a larger context. The standard technique is to
+ *       allocate each segment a range of values, based on the range of numbers used in that
+ *       segment. To convert a document number from a segment to an external value, the segment's
+ *       <i>base</i> document number is added. To convert an external value back to a
+ *       segment-specific value, the segment is identified by the range that the external value is
+ *       in, and the segment's base value is subtracted. For example two five document segments
+ *       might be combined, so that the first segment has a base value of zero, and the second of
+ *       five. Document three from the second segment would have an external value of eight.
+ *   <li>
+ *       <p>When documents are deleted, gaps are created in the numbering. These are eventually
+ *       removed as the index evolves through merging. Deleted documents are dropped when segments
+ *       are merged. A freshly-merged segment thus has no gaps in its numbering.
+ * </ul>
+ *
+ * </div> <a id="Overview"></a>
+ *
+ * <h3>Index Structure Overview</h3>
+ *
+ * <div>
+ *
+ * <p>Each segment index maintains the following:
+ *
+ * <ul>
+ *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat Segment info}. This
+ *       contains metadata about a segment, such as the number of documents, what files it uses, and
+ *       information about how the segment is sorted
+ *   <li>{@link org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat Field names}. This
+ *       contains metadata about the set of named fields used in the index.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Stored Field values}.
+ *       This contains, for each document, a list of attribute-value pairs, where the attributes are
+ *       field names. These are used to store auxiliary information about the document, such as its
+ *       title, url, or an identifier to access a database. The set of stored fields are what is
+ *       returned for each hit when searching. This is keyed by document number.
+ *   <li>{@link org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat Term dictionary}.
+ *       A dictionary containing all of the terms used in all of the indexed fields of all of the
+ *       documents. The dictionary also contains the number of documents which contain the term, and
+ *       pointers to the term's frequency and proximity data.
+ *   <li>{@link org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat Term Frequency
+ *       data}. For each term in the dictionary, the numbers of all the documents that contain that
+ *       term, and the frequency of the term in that document, unless frequencies are omitted
+ *       ({@link org.apache.lucene.index.IndexOptions#DOCS IndexOptions.DOCS})
+ *   <li>{@link org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat Term Proximity
+ *       data}. For each term in the dictionary, the positions that the term occurs in each
+ *       document. Note that this will not exist if all fields in all documents omit position data.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90NormsFormat Normalization factors}. For
+ *       each field in each document, a value is stored that is multiplied into the score for hits
+ *       on that field.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vectors}. For each
+ *       field in each document, the term vector (sometimes called document vector) may be stored. A
+ *       term vector consists of term text and term frequency. To add Term Vectors to your index see
+ *       the {@link org.apache.lucene.document.Field Field} constructors
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat Per-document values}. Like
+ *       stored values, these are also keyed by document number, but are generally intended to be
+ *       loaded into main memory for fast access. Whereas stored values are generally intended for
+ *       summary results from searches, per-document values are useful for things like scoring
+ *       factors.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat Live documents}. An
+ *       optional file indicating which documents are live.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90PointsFormat Point values}. Optional pair
+ *       of files, recording dimensionally indexed fields, to enable fast numeric range filtering
+ *       and large numeric values like BigInteger and BigDecimal (1D) and geographic shape
+ *       intersection (2D, 3D).
+ *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat Vector values}. The
+ *       vector format stores numeric vectors in a format optimized for random access and
+ *       computation, supporting high-dimensional nearest-neighbor search.
+ * </ul>
+ *
+ * <p>Details on each of these are provided in their linked pages. </div> <a id="File_Naming"></a>
+ *
+ * <h3>File Naming</h3>
+ *
+ * <div>
+ *
+ * <p>All files belonging to a segment have the same name with varying extensions. The extensions
+ * correspond to the different file formats described below. When using the Compound File format
+ * (default for small segments) these files (except for the Segment info file, the Lock file, and
+ * Deleted documents file) are collapsed into a single .cfs file (see below for details)
+ *
+ * <p>Typically, all segments in an index are stored in a single directory, although this is not
+ * required.
+ *
+ * <p>File names are never re-used. That is, when any file is saved to the Directory it is given a
+ * never before used filename. This is achieved using a simple generations approach. For example,
+ * the first segments file is segments_1, then segments_2, etc. The generation is a sequential long
+ * integer represented in alpha-numeric (base 36) form. </div> <a id="file-names"></a>
+ *
+ * <h3>Summary of File Extensions</h3>
+ *
+ * <div>
+ *
+ * <p>The following table summarizes the names and extensions of the files in Lucene:
+ *
+ * <table class="padding4" style="border-spacing: 1px; border-collapse: separate">
+ * <caption>lucene filenames by extension</caption>
+ * <tr>
+ * <th>Name</th>
+ * <th>Extension</th>
+ * <th>Brief Description</th>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.index.SegmentInfos Segments File}</td>
+ * <td>segments_N</td>
+ * <td>Stores information about a commit point</td>
+ * </tr>
+ * <tr>
+ * <td><a href="#Lock_File">Lock File</a></td>
+ * <td>write.lock</td>
+ * <td>The Write lock prevents multiple IndexWriters from writing to the same
+ * file.</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat Segment Info}</td>
+ * <td>.si</td>
+ * <td>Stores metadata about a segment</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90CompoundFormat Compound File}</td>
+ * <td>.cfs, .cfe</td>
+ * <td>An optional "virtual" file consisting of all the other index files for
+ * systems that frequently run out of file handles.</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat Fields}</td>
+ * <td>.fnm</td>
+ * <td>Stores information about the fields</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Field Index}</td>
+ * <td>.fdx</td>
+ * <td>Contains pointers to field data</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Field Data}</td>
+ * <td>.fdt</td>
+ * <td>The stored fields for documents</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat Term Dictionary}</td>
+ * <td>.tim</td>
+ * <td>The term dictionary, stores term info</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat Term Index}</td>
+ * <td>.tip</td>
+ * <td>The index into the Term Dictionary</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat Frequencies}</td>
+ * <td>.doc</td>
+ * <td>Contains the list of docs which contain each term along with frequency</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat Positions}</td>
+ * <td>.pos</td>
+ * <td>Stores position information about where a term occurs in the index</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat Payloads}</td>
+ * <td>.pay</td>
+ * <td>Stores additional per-position metadata information such as character offsets and user payloads</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90NormsFormat Norms}</td>
+ * <td>.nvd, .nvm</td>
+ * <td>Encodes length and boost factors for docs and fields</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat Per-Document Values}</td>
+ * <td>.dvd, .dvm</td>
+ * <td>Encodes additional scoring factors or other per-document information.</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vector Index}</td>
+ * <td>.tvx</td>
+ * <td>Stores offset into the document data file</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vector Data}</td>
+ * <td>.tvd</td>
+ * <td>Contains term vector data.</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat Live Documents}</td>
+ * <td>.liv</td>
+ * <td>Info about what documents are live</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90PointsFormat Point values}</td>
+ * <td>.dii, .dim</td>
+ * <td>Holds indexed points</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat Vector values}</td>
+ * <td>.vec, .vem, .veq, vex</td>
+ * <td>Holds indexed vectors; <code>.vec</code> files contain the raw vector data,
+ * <code>.vem</code> the vector metadata, <code>.veq</code> the quantized vector data, and <code>.vex</code> the
+ * hnsw graph data.</td>
+ * </tr>
+ * </table>
+ *
+ * </div> <a id="Lock_File"></a>
+ *
+ * <h3>Lock File</h3>
+ *
+ * The write lock, which is stored in the index directory by default, is named "write.lock". If the
+ * lock directory is different from the index directory then the write lock will be named
+ * "XXXX-write.lock" where XXXX is a unique prefix derived from the full path to the index
+ * directory. When this file is present, a writer is currently modifying the index (adding or
+ * removing documents). This lock file ensures that only one writer is modifying the index at a
+ * time. <a id="History"></a>
+ *
+ * <h3>History</h3>
+ *
+ * <p>Compatibility notes are provided in this document, describing how file formats have changed
+ * from prior versions:
+ *
+ * <ul>
+ *   <li>In version 2.1, the file format was changed to allow lock-less commits (ie, no more commit
+ *       lock). The change is fully backwards compatible: you can open a pre-2.1 index for searching
+ *       or adding/deleting of docs. When the new segments file is saved (committed), it will be
+ *       written in the new file format (meaning no specific "upgrade" process is needed). But note
+ *       that once a commit has occurred, pre-2.1 Lucene will not be able to read the index.
+ *   <li>In version 2.3, the file format was changed to allow segments to share a single set of doc
+ *       store (vectors &amp; stored fields) files. This allows for faster indexing in certain
+ *       cases. The change is fully backwards compatible (in the same way as the lock-less commits
+ *       change in 2.1).
+ *   <li>In version 2.4, Strings are now written as true UTF-8 byte sequence, not Java's modified
+ *       UTF-8. See <a href="http://issues.apache.org/jira/browse/LUCENE-510">LUCENE-510</a> for
+ *       details.
+ *   <li>In version 2.9, an optional opaque Map&lt;String,String&gt; CommitUserData may be passed to
+ *       IndexWriter's commit methods (and later retrieved), which is recorded in the segments_N
+ *       file. See <a href="http://issues.apache.org/jira/browse/LUCENE-1382">LUCENE-1382</a> for
+ *       details. Also, diagnostics were added to each segment written recording details about why
+ *       it was written (due to flush, merge; which OS/JRE was used; etc.). See issue <a
+ *       href="http://issues.apache.org/jira/browse/LUCENE-1654">LUCENE-1654</a> for details.
+ *   <li>In version 3.0, compressed fields are no longer written to the index (they can still be
+ *       read, but on merge the new segment will write them, uncompressed). See issue <a
+ *       href="http://issues.apache.org/jira/browse/LUCENE-1960">LUCENE-1960</a> for details.
+ *   <li>In version 3.1, segments records the code version that created them. See <a
+ *       href="http://issues.apache.org/jira/browse/LUCENE-2720">LUCENE-2720</a> for details.
+ *       Additionally segments track explicitly whether or not they have term vectors. See <a
+ *       href="http://issues.apache.org/jira/browse/LUCENE-2811">LUCENE-2811</a> for details.
+ *   <li>In version 3.2, numeric fields are written as natively to stored fields file, previously
+ *       they were stored in text format only.
+ *   <li>In version 3.4, fields can omit position data while still indexing term frequencies.
+ *   <li>In version 4.0, the format of the inverted index became extensible via the {@link
+ *       org.apache.lucene.codecs.Codec Codec} api. Fast per-document storage ({@code DocValues})
+ *       was introduced. Normalization factors need no longer be a single byte, they can be any
+ *       {@link org.apache.lucene.index.NumericDocValues NumericDocValues}. Terms need not be
+ *       unicode strings, they can be any byte sequence. Term offsets can optionally be indexed into
+ *       the postings lists. Payloads can be stored in the term vectors.
+ *   <li>In version 4.1, the format of the postings list changed to use either of FOR compression or
+ *       variable-byte encoding, depending upon the frequency of the term. Terms appearing only once
+ *       were changed to inline directly into the term dictionary. Stored fields are compressed by
+ *       default.
+ *   <li>In version 4.2, term vectors are compressed by default. DocValues has a new multi-valued
+ *       type (SortedSet), that can be used for faceting/grouping/joining on multi-valued fields.
+ *   <li>In version 4.5, DocValues were extended to explicitly represent missing values.
+ *   <li>In version 4.6, FieldInfos were extended to support per-field DocValues generation, to
+ *       allow updating NumericDocValues fields.
+ *   <li>In version 4.8, checksum footers were added to the end of each index file for improved data
+ *       integrity. Specifically, the last 8 bytes of every index file contain the zlib-crc32
+ *       checksum of the file.
+ *   <li>In version 4.9, DocValues has a new multi-valued numeric type (SortedNumeric) that is
+ *       suitable for faceting/sorting/analytics.
+ *   <li>In version 5.4, DocValues have been improved to store more information on disk: addresses
+ *       for binary fields and ord indexes for multi-valued fields.
+ *   <li>In version 6.0, Points were added, for multi-dimensional range/distance search.
+ *   <li>In version 6.2, new Segment info format that reads/writes the index sort, to support index
+ *       sorting.
+ *   <li>In version 7.0, DocValues have been improved to better support sparse doc values thanks to
+ *       an iterator API.
+ *   <li>In version 8.0, postings have been enhanced to record, for each block of doc ids, the (term
+ *       freq, normalization factor) pairs that may trigger the maximum score of the block. This
+ *       information is recorded alongside skip data in order to be able to skip blocks of doc ids
+ *       if they may not produce high enough scores. Additionally doc values and norms has been
+ *       extended with jump-tables to make access O(1) instead of O(n), where n is the number of
+ *       elements to skip when advancing in the data.
+ *   <li>In version 8.4, postings, positions, offsets and payload lengths have move to a more
+ *       performant encoding that is vectorized.
+ *   <li>In version 8.6, index sort serialization is delegated to the sorts themselves, to allow
+ *       user-defined sorts to be used
+ *   <li>In version 8.7, stored fields compression became adaptive to better handle documents with
+ *       smaller stored fields.
+ *   <li>In version 9.0, vector-valued fields were added.
+ *   <li>In version 9.1, vector-valued fields were modified to add a graph hierarchy.
+ *   <li>In version 9.2, docs of vector-valued fields were moved from .vem to .vec and encoded by
+ *       IndexDISI. ordToDoc mappings was added to .vem.
+ *   <li>In version 9.5, HNSW graph connections were changed to be delta-encoded with vints.
+ *       Additionally, metadata file size improvements were made by delta-encoding nodes by graph
+ *       layer and not writing the node ids for the zeroth layer.
+ *   <li>In version 9.9, Vector scalar quantization support was added. Allowing the HNSW vector
+ *       format to utilize int8 quantized vectors for float32 vector search.
+ * </ul>
+ *
+ * <a id="Limitations"></a>
+ *
+ * <h3>Limitations</h3>
+ *
+ * <div>
+ *
+ * <p>Lucene uses a Java <code>int</code> to refer to document numbers, and the index file format
+ * uses an <code>Int32</code> on-disk to store document numbers. This is a limitation of both the
+ * index file format and the current implementation. Eventually these should be replaced with either
+ * <code>UInt64</code> values, or better yet, {@link org.apache.lucene.store.DataOutput#writeVInt
+ * VInt} values which have no limit. </div>
+ */
+package org.apache.lucene.backward_codecs.lucene99;

lucene/backward-codecs/src/resources/META-INF/services/org.apache.lucene.codecs.Codec

@@ -22,3 +22,4 @@ org.apache.lucene.backward_codecs.lucene91.Lucene91Codec
 org.apache.lucene.backward_codecs.lucene92.Lucene92Codec
 org.apache.lucene.backward_codecs.lucene94.Lucene94Codec
 org.apache.lucene.backward_codecs.lucene95.Lucene95Codec
+org.apache.lucene.backward_codecs.lucene99.Lucene99Codec

lucene/backward-codecs/src/resources/META-INF/services/org.apache.lucene.codecs.PostingsFormat

@@ -16,3 +16,4 @@
 org.apache.lucene.backward_codecs.lucene50.Lucene50PostingsFormat
 org.apache.lucene.backward_codecs.lucene84.Lucene84PostingsFormat
 org.apache.lucene.backward_codecs.lucene90.Lucene90PostingsFormat
+org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene90/TestLucene90PostingsFormat.java

@@ -23,12 +23,11 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import org.apache.lucene.backward_codecs.lucene90.Lucene90ScoreSkipReader.MutableImpactList;
+import org.apache.lucene.backward_codecs.lucene99.Lucene99SkipWriter;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.CompetitiveImpactAccumulator;
 import org.apache.lucene.codecs.lucene90.blocktree.FieldReader;
 import org.apache.lucene.codecs.lucene90.blocktree.Stats;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat;
-import org.apache.lucene.codecs.lucene99.Lucene99SkipWriter;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
 import org.apache.lucene.index.DirectoryReader;
@@ -77,22 +76,6 @@ public class TestLucene90PostingsFormat extends BasePostingsFormatTestCase {
     d.close();
   }
 
-  private void shouldFail(int minItemsInBlock, int maxItemsInBlock) {
-    expectThrows(
-        IllegalArgumentException.class,
-        () -> {
-          new Lucene99PostingsFormat(minItemsInBlock, maxItemsInBlock);
-        });
-  }
-
-  public void testInvalidBlockSizes() throws Exception {
-    shouldFail(0, 0);
-    shouldFail(10, 8);
-    shouldFail(-1, 10);
-    shouldFail(10, -1);
-    shouldFail(10, 12);
-  }
-
   public void testImpactSerialization() throws IOException {
     // omit norms and omit freqs
     doTestImpactSerialization(Collections.singletonList(new Impact(1, 1L)));

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene94/Lucene94HnswVectorsWriter.java

@@ -693,9 +693,9 @@ public final class Lucene94HnswVectorsWriter extends KnnVectorsWriter {
       lastDocID = docID;
     }
 
-    OnHeapHnswGraph getGraph() {
+    OnHeapHnswGraph getGraph() throws IOException {
       if (vectors.size() > 0) {
-        return hnswGraphBuilder.getGraph();
+        return hnswGraphBuilder.getCompletedGraph();
       } else {
         return null;
       }

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene95/Lucene95HnswVectorsWriter.java

@@ -732,9 +732,9 @@ public final class Lucene95HnswVectorsWriter extends KnnVectorsWriter {
       lastDocID = docID;
     }
 
-    OnHeapHnswGraph getGraph() {
+    OnHeapHnswGraph getGraph() throws IOException {
       if (vectors.size() > 0) {
-        return hnswGraphBuilder.getGraph();
+        return hnswGraphBuilder.getCompletedGraph();
       } else {
         return null;
       }

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene99/Lucene99PostingsWriter.java

@@ -14,22 +14,22 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
-import static org.apache.lucene.codecs.lucene99.ForUtil.BLOCK_SIZE;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.DOC_CODEC;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.MAX_SKIP_LEVELS;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.PAY_CODEC;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.POS_CODEC;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.TERMS_CODEC;
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.VERSION_CURRENT;
+import static org.apache.lucene.backward_codecs.lucene99.ForUtil.BLOCK_SIZE;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.DOC_CODEC;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.MAX_SKIP_LEVELS;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.PAY_CODEC;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.POS_CODEC;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.TERMS_CODEC;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.VERSION_CURRENT;
 
 import java.io.IOException;
+import org.apache.lucene.backward_codecs.lucene99.Lucene99PostingsFormat.IntBlockTermState;
 import org.apache.lucene.codecs.BlockTermState;
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.codecs.CompetitiveImpactAccumulator;
 import org.apache.lucene.codecs.PushPostingsWriterBase;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.IntBlockTermState;
 import org.apache.lucene.index.CorruptIndexException;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.IndexFileNames;

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene99/Lucene99RWPostingsFormat.java

@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.backward_codecs.lucene99;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.FieldsConsumer;
+import org.apache.lucene.codecs.PostingsWriterBase;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
+import org.apache.lucene.index.SegmentWriteState;
+import org.apache.lucene.util.IOUtils;
+
+public class Lucene99RWPostingsFormat extends Lucene99PostingsFormat {
+
+  private final int minTermBlockSize;
+  private final int maxTermBlockSize;
+
+  /** Creates {@code Lucene99PostingsFormat} with default settings. */
+  public Lucene99RWPostingsFormat() {
+    this(
+        Lucene90BlockTreeTermsWriter.DEFAULT_MIN_BLOCK_SIZE,
+        Lucene90BlockTreeTermsWriter.DEFAULT_MAX_BLOCK_SIZE);
+  }
+
+  /**
+   * Creates {@code Lucene99PostingsFormat} with custom values for {@code minBlockSize} and {@code
+   * maxBlockSize} passed to block terms dictionary.
+   *
+   * @see
+   *     Lucene90BlockTreeTermsWriter#Lucene90BlockTreeTermsWriter(SegmentWriteState,PostingsWriterBase,int,int)
+   */
+  public Lucene99RWPostingsFormat(int minTermBlockSize, int maxTermBlockSize) {
+    super();
+    Lucene90BlockTreeTermsWriter.validateSettings(minTermBlockSize, maxTermBlockSize);
+    this.minTermBlockSize = minTermBlockSize;
+    this.maxTermBlockSize = maxTermBlockSize;
+  }
+
+  @Override
+  public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
+    PostingsWriterBase postingsWriter = new Lucene99PostingsWriter(state);
+    boolean success = false;
+    try {
+      FieldsConsumer ret =
+          new Lucene90BlockTreeTermsWriter(
+              state, postingsWriter, minTermBlockSize, maxTermBlockSize);
+      success = true;
+      return ret;
+    } finally {
+      if (!success) {
+        IOUtils.closeWhileHandlingException(postingsWriter);
+      }
+    }
+  }
+}

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene99/TestForDeltaUtil.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import com.carrotsearch.randomizedtesting.generators.RandomNumbers;
 import java.io.IOException;

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene99/TestForUtil.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import com.carrotsearch.randomizedtesting.generators.RandomNumbers;
 import java.io.IOException;

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene99/TestLucene99HnswScalarQuantizedVectorsFormat.java

@@ -19,7 +19,6 @@ package org.apache.lucene.backward_codecs.lucene99;
 
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.KnnVectorsFormat;
-import org.apache.lucene.codecs.lucene99.Lucene99Codec;
 import org.apache.lucene.tests.index.BaseKnnVectorsFormatTestCase;
 
 public class TestLucene99HnswScalarQuantizedVectorsFormat extends BaseKnnVectorsFormatTestCase {

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene99/TestLucene99PostingsFormat.java

@@ -14,22 +14,26 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
-import static org.apache.lucene.codecs.lucene99.Lucene99ScoreSkipReader.readImpacts;
+import static org.apache.lucene.backward_codecs.lucene99.Lucene99ScoreSkipReader.readImpacts;
 
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import org.apache.lucene.backward_codecs.lucene99.Lucene99ScoreSkipReader.MutableImpactList;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.CompetitiveImpactAccumulator;
 import org.apache.lucene.codecs.lucene90.blocktree.FieldReader;
 import org.apache.lucene.codecs.lucene90.blocktree.Stats;
-import org.apache.lucene.codecs.lucene99.Lucene99ScoreSkipReader.MutableImpactList;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
-import org.apache.lucene.index.*;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.Impact;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.store.ByteArrayDataInput;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.IOContext;
@@ -41,7 +45,7 @@ import org.apache.lucene.tests.util.TestUtil;
 import org.apache.lucene.util.BytesRef;
 
 public class TestLucene99PostingsFormat extends BasePostingsFormatTestCase {
-  private final Codec codec = TestUtil.alwaysPostingsFormat(new Lucene99PostingsFormat());
+  private final Codec codec = TestUtil.alwaysPostingsFormat(new Lucene99RWPostingsFormat());
 
   @Override
   protected Codec getCodec() {
@@ -77,7 +81,7 @@ public class TestLucene99PostingsFormat extends BasePostingsFormatTestCase {
     expectThrows(
         IllegalArgumentException.class,
         () -> {
-          new Lucene99PostingsFormat(minItemsInBlock, maxItemsInBlock);
+          new Lucene99RWPostingsFormat(minItemsInBlock, maxItemsInBlock);
         });
   }
 

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene99/TestPForUtil.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.apache.lucene.codecs.lucene99;
+package org.apache.lucene.backward_codecs.lucene99;
 
 import com.carrotsearch.randomizedtesting.generators.RandomNumbers;
 import java.io.IOException;

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene99/TestPostingsUtil.java

@@ -0,0 +1,49 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.backward_codecs.lucene99;
+
+import java.io.IOException;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IOContext;
+import org.apache.lucene.store.IndexInput;
+import org.apache.lucene.store.IndexOutput;
+import org.apache.lucene.tests.util.LuceneTestCase;
+
+public class TestPostingsUtil extends LuceneTestCase {
+
+  // checks for bug described in https://github.com/apache/lucene/issues/13373
+  public void testIntegerOverflow() throws IOException {
+    final int size = random().nextInt(1, ForUtil.BLOCK_SIZE);
+    final long[] docDeltaBuffer = new long[size];
+    final long[] freqBuffer = new long[size];
+
+    final int delta = 1 << 30;
+    docDeltaBuffer[0] = delta;
+    try (Directory dir = newDirectory()) {
+      try (IndexOutput out = dir.createOutput("test", IOContext.DEFAULT)) {
+        // In old implementation, this would cause integer overflow exception.
+        PostingsUtil.writeVIntBlock(out, docDeltaBuffer, freqBuffer, size, true);
+      }
+      long[] restoredDocs = new long[size];
+      long[] restoredFreqs = new long[size];
+      try (IndexInput in = dir.openInput("test", IOContext.DEFAULT)) {
+        PostingsUtil.readVIntBlock(in, restoredDocs, restoredFreqs, size, true, true);
+      }
+      assertEquals(delta, restoredDocs[0]);
+    }
+  }
+}

lucene/backward-codecs/src/test/org/apache/lucene/backward_index/TestInt8HnswBackwardsCompatibility.java

@@ -20,9 +20,9 @@ import static org.apache.lucene.backward_index.TestBasicBackwardsCompatibility.a
 
 import com.carrotsearch.randomizedtesting.annotations.ParametersFactory;
 import java.io.IOException;
+import org.apache.lucene.backward_codecs.lucene99.Lucene99Codec;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.KnnVectorsFormat;
-import org.apache.lucene.codecs.lucene99.Lucene99Codec;
 import org.apache.lucene.codecs.lucene99.Lucene99HnswScalarQuantizedVectorsFormat;
 import org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat;
 import org.apache.lucene.document.Document;

lucene/benchmark-jmh/src/java/org/apache/lucene/benchmark/jmh/PostingIndexInputBenchmark.java

@@ -0,0 +1,106 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.benchmark.jmh;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Random;
+import java.util.concurrent.TimeUnit;
+import org.apache.lucene.codecs.lucene912.ForUtil;
+import org.apache.lucene.codecs.lucene912.PostingIndexInput;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IOContext;
+import org.apache.lucene.store.IndexInput;
+import org.apache.lucene.store.IndexOutput;
+import org.apache.lucene.store.MMapDirectory;
+import org.apache.lucene.util.IOUtils;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.TearDown;
+import org.openjdk.jmh.annotations.Warmup;
+import org.openjdk.jmh.infra.Blackhole;
+
+@BenchmarkMode(Mode.Throughput)
+@OutputTimeUnit(TimeUnit.MICROSECONDS)
+@State(Scope.Benchmark)
+@Warmup(iterations = 5, time = 1)
+@Measurement(iterations = 5, time = 1)
+@Fork(
+    value = 3,
+    jvmArgsAppend = {"-Xmx1g", "-Xms1g", "-XX:+AlwaysPreTouch"})
+public class PostingIndexInputBenchmark {
+
+  private Path path;
+  private Directory dir;
+  private IndexInput in;
+  private PostingIndexInput postingIn;
+  private final ForUtil forUtil = new ForUtil();
+  private final long[] values = new long[128];
+
+  @Param({"5", "6", "7", "8", "9", "10"})
+  public int bpv;
+
+  @Setup(Level.Trial)
+  public void setup() throws Exception {
+    path = Files.createTempDirectory("forUtil");
+    dir = MMapDirectory.open(path);
+    try (IndexOutput out = dir.createOutput("docs", IOContext.DEFAULT)) {
+      Random r = new Random(0);
+      // Write enough random data to not reach EOF while decoding
+      for (int i = 0; i < 100; ++i) {
+        out.writeLong(r.nextLong());
+      }
+    }
+    in = dir.openInput("docs", IOContext.DEFAULT);
+    postingIn = new PostingIndexInput(in, forUtil);
+  }
+
+  @TearDown(Level.Trial)
+  public void tearDown() throws Exception {
+    if (dir != null) {
+      dir.deleteFile("docs");
+    }
+    IOUtils.close(in, dir);
+    in = null;
+    dir = null;
+    Files.deleteIfExists(path);
+  }
+
+  @Benchmark
+  public void decode(Blackhole bh) throws IOException {
+    in.seek(3); // random unaligned offset
+    postingIn.decode(bpv, values);
+    bh.consume(values);
+  }
+
+  @Benchmark
+  public void decodeAndPrefixSum(Blackhole bh) throws IOException {
+    in.seek(3); // random unaligned offset
+    postingIn.decodeAndPrefixSum(bpv, 100, values);
+    bh.consume(values);
+  }
+}

lucene/benchmark/src/java/org/apache/lucene/benchmark/byTask/tasks/SearchWithCollectorTask.java

@@ -20,7 +20,7 @@ import org.apache.lucene.benchmark.byTask.PerfRunData;
 import org.apache.lucene.benchmark.byTask.feeds.QueryMaker;
 import org.apache.lucene.benchmark.byTask.utils.Config;
 import org.apache.lucene.search.Collector;
-import org.apache.lucene.search.TopScoreDocCollector;
+import org.apache.lucene.search.TopScoreDocCollectorManager;
 
 /** Does search w/ a custom collector */
 public class SearchWithCollectorTask extends SearchTask {
@@ -49,7 +49,8 @@ public class SearchWithCollectorTask extends SearchTask {
   protected Collector createCollector() throws Exception {
     Collector collector = null;
     if (clnName.equalsIgnoreCase("topScoreDoc") == true) {
-      collector = TopScoreDocCollector.create(numHits(), Integer.MAX_VALUE);
+      collector =
+          new TopScoreDocCollectorManager(numHits(), null, Integer.MAX_VALUE, false).newCollector();
     } else if (clnName.length() > 0) {
       collector = Class.forName(clnName).asSubclass(Collector.class).getConstructor().newInstance();
 

lucene/codecs/src/java/org/apache/lucene/codecs/blocktreeords/BlockTreeOrdsPostingsFormat.java

@@ -23,13 +23,13 @@ import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.PostingsReaderBase;
 import org.apache.lucene.codecs.PostingsWriterBase;
 import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsReader;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsWriter;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsReader;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsWriter;
 import org.apache.lucene.index.SegmentReadState;
 import org.apache.lucene.index.SegmentWriteState;
 import org.apache.lucene.util.IOUtils;
 
-/** Uses {@link OrdsBlockTreeTermsWriter} with {@link Lucene99PostingsWriter}. */
+/** Uses {@link OrdsBlockTreeTermsWriter} with {@link Lucene912PostingsWriter}. */
 public class BlockTreeOrdsPostingsFormat extends PostingsFormat {
 
   private final int minTermBlockSize;
@@ -67,7 +67,7 @@ public class BlockTreeOrdsPostingsFormat extends PostingsFormat {
 
   @Override
   public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
-    PostingsWriterBase postingsWriter = new Lucene99PostingsWriter(state);
+    PostingsWriterBase postingsWriter = new Lucene912PostingsWriter(state);
 
     boolean success = false;
     try {
@@ -84,7 +84,7 @@ public class BlockTreeOrdsPostingsFormat extends PostingsFormat {
 
   @Override
   public FieldsProducer fieldsProducer(SegmentReadState state) throws IOException {
-    PostingsReaderBase postingsReader = new Lucene99PostingsReader(state);
+    PostingsReaderBase postingsReader = new Lucene912PostingsReader(state);
     boolean success = false;
     try {
       FieldsProducer ret = new OrdsBlockTreeTermsReader(postingsReader, state);

lucene/codecs/src/java/org/apache/lucene/codecs/memory/DirectPostingsFormat.java

@@ -24,7 +24,7 @@ import java.util.TreeMap;
 import org.apache.lucene.codecs.FieldsConsumer;
 import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.PostingsFormat;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat;
 import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.Fields;
@@ -54,7 +54,7 @@ import org.apache.lucene.util.automaton.TransitionAccessor;
 //   - or: longer dense skip lists than just next byte?
 
 /**
- * Wraps {@link Lucene99PostingsFormat} format for on-disk storage, but then at read time loads and
+ * Wraps {@link Lucene912PostingsFormat} format for on-disk storage, but then at read time loads and
  * stores all terms and postings directly in RAM as byte[], int[].
  *
  * <p><b>WARNING</b>: This is exceptionally RAM intensive: it makes no effort to compress the
@@ -97,12 +97,12 @@ public final class DirectPostingsFormat extends PostingsFormat {
 
   @Override
   public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
-    return PostingsFormat.forName("Lucene99").fieldsConsumer(state);
+    return PostingsFormat.forName("Lucene912").fieldsConsumer(state);
   }
 
   @Override
   public FieldsProducer fieldsProducer(SegmentReadState state) throws IOException {
-    FieldsProducer postings = PostingsFormat.forName("Lucene99").fieldsProducer(state);
+    FieldsProducer postings = PostingsFormat.forName("Lucene912").fieldsProducer(state);
     if (state.context.context() != IOContext.Context.MERGE) {
       FieldsProducer loadedPostings;
       try {

lucene/codecs/src/java/org/apache/lucene/codecs/memory/FSTPostingsFormat.java

@@ -22,8 +22,8 @@ import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.PostingsReaderBase;
 import org.apache.lucene.codecs.PostingsWriterBase;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsReader;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsWriter;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsReader;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsWriter;
 import org.apache.lucene.index.SegmentReadState;
 import org.apache.lucene.index.SegmentWriteState;
 import org.apache.lucene.util.IOUtils;
@@ -41,7 +41,7 @@ public final class FSTPostingsFormat extends PostingsFormat {
 
   @Override
   public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
-    PostingsWriterBase postingsWriter = new Lucene99PostingsWriter(state);
+    PostingsWriterBase postingsWriter = new Lucene912PostingsWriter(state);
 
     boolean success = false;
     try {
@@ -57,7 +57,7 @@ public final class FSTPostingsFormat extends PostingsFormat {
 
   @Override
   public FieldsProducer fieldsProducer(SegmentReadState state) throws IOException {
-    PostingsReaderBase postingsReader = new Lucene99PostingsReader(state);
+    PostingsReaderBase postingsReader = new Lucene912PostingsReader(state);
     boolean success = false;
     try {
       FieldsProducer ret = new FSTTermsReader(state, postingsReader);

lucene/codecs/src/java/org/apache/lucene/codecs/uniformsplit/DeltaBaseTermStateSerializer.java

@@ -17,13 +17,13 @@
 
 package org.apache.lucene.codecs.uniformsplit;
 
-import static org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.BLOCK_SIZE;
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.BLOCK_SIZE;
 
 import java.io.IOException;
 import org.apache.lucene.codecs.BlockTermState;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.IntBlockTermState;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsReader;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsWriter;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.IntBlockTermState;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsReader;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsWriter;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.TermState;
@@ -34,7 +34,7 @@ import org.apache.lucene.util.RamUsageEstimator;
 
 /**
  * {@link TermState} serializer which encodes each file pointer as a delta relative to a base file
- * pointer. It differs from {@link Lucene99PostingsWriter#encodeTerm} which encodes each file
+ * pointer. It differs from {@link Lucene912PostingsWriter#encodeTerm} which encodes each file
  * pointer as a delta relative to the previous file pointer.
  *
  * <p>It automatically sets the base file pointer to the first valid file pointer for doc start FP,
@@ -95,7 +95,7 @@ public class DeltaBaseTermStateSerializer implements Accountable {
   /**
    * Writes a {@link BlockTermState} to the provided {@link DataOutput}.
    *
-   * <p>Simpler variant of {@link Lucene99PostingsWriter#encodeTerm(DataOutput, FieldInfo,
+   * <p>Simpler variant of {@link Lucene912PostingsWriter#encodeTerm(DataOutput, FieldInfo,
    * BlockTermState, boolean)}.
    */
   public void writeTermState(
@@ -140,15 +140,12 @@ public class DeltaBaseTermStateSerializer implements Accountable {
         termStatesOutput.writeVLong(intTermState.lastPosBlockOffset);
       }
     }
-    if (intTermState.skipOffset != -1) {
-      termStatesOutput.writeVLong(intTermState.skipOffset);
-    }
   }
 
   /**
    * Reads a {@link BlockTermState} from the provided {@link DataInput}.
    *
-   * <p>Simpler variant of {@link Lucene99PostingsReader#decodeTerm(DataInput, FieldInfo,
+   * <p>Simpler variant of {@link Lucene912PostingsReader#decodeTerm(DataInput, FieldInfo,
    * BlockTermState, boolean)}.
    *
    * @param reuse {@link BlockTermState} to reuse; or null to create a new one.
@@ -190,9 +187,6 @@ public class DeltaBaseTermStateSerializer implements Accountable {
         intTermState.lastPosBlockOffset = termStatesInput.readVLong();
       }
     }
-    if (intTermState.docFreq > BLOCK_SIZE) {
-      intTermState.skipOffset = termStatesInput.readVLong();
-    }
     return intTermState;
   }
 
@@ -210,7 +204,6 @@ public class DeltaBaseTermStateSerializer implements Accountable {
     termState.docStartFP = 0;
     termState.posStartFP = 0;
     termState.payStartFP = 0;
-    termState.skipOffset = -1;
     termState.lastPosBlockOffset = -1;
     termState.singletonDocID = -1;
 

lucene/codecs/src/java/org/apache/lucene/codecs/uniformsplit/UniformSplitPostingsFormat.java

@@ -23,8 +23,8 @@ import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.PostingsReaderBase;
 import org.apache.lucene.codecs.PostingsWriterBase;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsReader;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsWriter;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsReader;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsWriter;
 import org.apache.lucene.index.SegmentReadState;
 import org.apache.lucene.index.SegmentWriteState;
 import org.apache.lucene.util.IOUtils;
@@ -113,7 +113,7 @@ public class UniformSplitPostingsFormat extends PostingsFormat {
 
   @Override
   public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
-    PostingsWriterBase postingsWriter = new Lucene99PostingsWriter(state);
+    PostingsWriterBase postingsWriter = new Lucene912PostingsWriter(state);
     boolean success = false;
     try {
       FieldsConsumer termsWriter =
@@ -130,7 +130,7 @@ public class UniformSplitPostingsFormat extends PostingsFormat {
 
   @Override
   public FieldsProducer fieldsProducer(SegmentReadState state) throws IOException {
-    PostingsReaderBase postingsReader = new Lucene99PostingsReader(state);
+    PostingsReaderBase postingsReader = new Lucene912PostingsReader(state);
     boolean success = false;
     try {
       FieldsProducer termsReader =

lucene/codecs/src/java/org/apache/lucene/codecs/uniformsplit/package-info.java

@@ -28,7 +28,7 @@
  *       org.apache.lucene.search.PhraseQuery})
  *   <li>Quite efficient for {@link org.apache.lucene.search.PrefixQuery}
  *   <li>Not efficient for spell-check and {@link org.apache.lucene.search.FuzzyQuery}, in this case
- *       prefer {@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat}
+ *       prefer {@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat}
  * </ul>
  */
 package org.apache.lucene.codecs.uniformsplit;

lucene/codecs/src/test/org/apache/lucene/codecs/bitvectors/TestHnswBitVectorsFormat.java

@@ -22,7 +22,7 @@ import java.io.IOException;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.FilterCodec;
 import org.apache.lucene.codecs.KnnVectorsFormat;
-import org.apache.lucene.codecs.lucene99.Lucene99Codec;
+import org.apache.lucene.codecs.lucene912.Lucene912Codec;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
 import org.apache.lucene.document.KnnByteVectorField;
@@ -42,7 +42,7 @@ import org.apache.lucene.tests.index.BaseIndexFileFormatTestCase;
 public class TestHnswBitVectorsFormat extends BaseIndexFileFormatTestCase {
   @Override
   protected Codec getCodec() {
-    return new Lucene99Codec() {
+    return new Lucene912Codec() {
       @Override
       public KnnVectorsFormat getKnnVectorsFormatForField(String field) {
         return new HnswBitVectorsFormat();

lucene/codecs/src/test/org/apache/lucene/codecs/lucene90/tests/MockTermStateFactory.java

@@ -17,7 +17,7 @@
 
 package org.apache.lucene.codecs.lucene90.tests;
 
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat.IntBlockTermState;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.IntBlockTermState;
 
 /** Test utility class to create mock {@link IntBlockTermState}. */
 public class MockTermStateFactory {

lucene/core/src/generated/checksums/generateForUtil.json

@@ -1,4 +1,4 @@
 {
-    "lucene/core/src/java/org/apache/lucene/codecs/lucene99/ForUtil.java": "1292ad354d255b1272ffd3db684aa2ddb2bc49ec",
-    "lucene/core/src/java/org/apache/lucene/codecs/lucene99/gen_ForUtil.py": "ab7b63a1b73986cc04e43de1c8f474b97aef5116"
+    "lucene/core/src/java/org/apache/lucene/codecs/lucene912/ForUtil.java": "cc7d40997e2d6500b79c19ff47461ed6e89d2268",
+    "lucene/core/src/java/org/apache/lucene/codecs/lucene912/gen_ForUtil.py": "ba029f2e374e66c6cf315b2c93f4efa6944dfbb8"
 }

lucene/core/src/java/module-info.java

@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-import org.apache.lucene.codecs.lucene99.Lucene99Codec;
+import org.apache.lucene.codecs.lucene912.Lucene912Codec;
 
 /** Lucene Core. */
 @SuppressWarnings("module") // the test framework is compiled after the core...
@@ -33,6 +33,7 @@ module org.apache.lucene.core {
   exports org.apache.lucene.codecs.lucene94;
   exports org.apache.lucene.codecs.lucene95;
   exports org.apache.lucene.codecs.lucene99;
+  exports org.apache.lucene.codecs.lucene912;
   exports org.apache.lucene.codecs.perfield;
   exports org.apache.lucene.codecs;
   exports org.apache.lucene.document;
@@ -71,7 +72,7 @@ module org.apache.lucene.core {
   provides org.apache.lucene.analysis.TokenizerFactory with
       org.apache.lucene.analysis.standard.StandardTokenizerFactory;
   provides org.apache.lucene.codecs.Codec with
-      Lucene99Codec;
+      Lucene912Codec;
   provides org.apache.lucene.codecs.DocValuesFormat with
       org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat;
   provides org.apache.lucene.codecs.KnnVectorsFormat with
@@ -79,7 +80,7 @@ module org.apache.lucene.core {
       org.apache.lucene.codecs.lucene99.Lucene99HnswScalarQuantizedVectorsFormat,
       org.apache.lucene.codecs.lucene99.Lucene99ScalarQuantizedVectorsFormat;
   provides org.apache.lucene.codecs.PostingsFormat with
-      org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat;
+      org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat;
   provides org.apache.lucene.index.SortFieldProvider with
       org.apache.lucene.search.SortField.Provider,
       org.apache.lucene.search.SortedNumericSortField.Provider,

lucene/core/src/java/org/apache/lucene/codecs/Codec.java

@@ -55,7 +55,7 @@ public abstract class Codec implements NamedSPILoader.NamedSPI {
       return LOADER;
     }
 
-    static Codec defaultCodec = LOADER.lookup("Lucene99");
+    static Codec defaultCodec = LOADER.lookup("Lucene912");
   }
 
   private final String name;

lucene/core/src/java/org/apache/lucene/codecs/CompetitiveImpactAccumulator.java

@@ -18,8 +18,6 @@ package org.apache.lucene.codecs;
 
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collection;
-import java.util.Collections;
 import java.util.Comparator;
 import java.util.Iterator;
 import java.util.List;
@@ -106,7 +104,7 @@ public final class CompetitiveImpactAccumulator {
   }
 
   /** Get the set of competitive freq and norm pairs, ordered by increasing freq and norm. */
-  public Collection<Impact> getCompetitiveFreqNormPairs() {
+  public List<Impact> getCompetitiveFreqNormPairs() {
     List<Impact> impacts = new ArrayList<>();
     int maxFreqForLowerNorms = 0;
     for (int i = 0; i < maxFreqs.length; ++i) {
@@ -126,7 +124,7 @@ public final class CompetitiveImpactAccumulator {
     for (Impact impact : impacts) {
       add(impact, freqNormPairs);
     }
-    return Collections.unmodifiableSet(freqNormPairs);
+    return List.copyOf(freqNormPairs);
   }
 
   private void add(Impact newEntry, TreeSet<Impact> freqNormPairs) {

lucene/core/src/java/org/apache/lucene/codecs/KnnVectorsWriter.java

@@ -23,6 +23,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
+import java.util.function.BiFunction;
 import org.apache.lucene.index.ByteVectorValues;
 import org.apache.lucene.index.DocIDMerger;
 import org.apache.lucene.index.DocsWithFieldSet;
@@ -35,6 +36,7 @@ import org.apache.lucene.internal.hppc.IntIntHashMap;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.VectorScorer;
 import org.apache.lucene.util.Accountable;
+import org.apache.lucene.util.IOFunction;
 
 /** Writes vectors to an index. */
 public abstract class KnnVectorsWriter implements Accountable, Closeable {
@@ -111,11 +113,11 @@ public abstract class KnnVectorsWriter implements Accountable, Closeable {
   }
 
   /** Tracks state of one sub-reader that we are merging */
-  private static class VectorValuesSub extends DocIDMerger.Sub {
+  private static class FloatVectorValuesSub extends DocIDMerger.Sub {
 
     final FloatVectorValues values;
 
-    VectorValuesSub(MergeState.DocMap docMap, FloatVectorValues values) {
+    FloatVectorValuesSub(MergeState.DocMap docMap, FloatVectorValues values) {
       super(docMap);
       this.values = values;
       assert values.docID() == -1;
@@ -201,61 +203,81 @@ public abstract class KnnVectorsWriter implements Accountable, Closeable {
   public static final class MergedVectorValues {
     private MergedVectorValues() {}
 
-    /** Returns a merged view over all the segment's {@link FloatVectorValues}. */
-    public static FloatVectorValues mergeFloatVectorValues(
-        FieldInfo fieldInfo, MergeState mergeState) throws IOException {
+    private static void validateFieldEncoding(FieldInfo fieldInfo, VectorEncoding expected) {
       assert fieldInfo != null && fieldInfo.hasVectorValues();
-      if (fieldInfo.getVectorEncoding() != VectorEncoding.FLOAT32) {
+      VectorEncoding fieldEncoding = fieldInfo.getVectorEncoding();
+      if (fieldEncoding != expected) {
         throw new UnsupportedOperationException(
-            "Cannot merge vectors encoded as [" + fieldInfo.getVectorEncoding() + "] as FLOAT32");
+            "Cannot merge vectors encoded as [" + fieldEncoding + "] as " + expected);
       }
-      List<VectorValuesSub> subs = new ArrayList<>();
-      for (int i = 0; i < mergeState.knnVectorsReaders.length; i++) {
-        KnnVectorsReader knnVectorsReader = mergeState.knnVectorsReaders[i];
+    }
+
+    private static <V, S> List<S> mergeVectorValues(
+        KnnVectorsReader[] knnVectorsReaders,
+        MergeState.DocMap[] docMaps,
+        IOFunction<KnnVectorsReader, V> valuesSupplier,
+        BiFunction<MergeState.DocMap, V, S> newSub)
+        throws IOException {
+      List<S> subs = new ArrayList<>();
+      for (int i = 0; i < knnVectorsReaders.length; i++) {
+        KnnVectorsReader knnVectorsReader = knnVectorsReaders[i];
         if (knnVectorsReader != null) {
-          FloatVectorValues values = knnVectorsReader.getFloatVectorValues(fieldInfo.name);
+          V values = valuesSupplier.apply(knnVectorsReader);
           if (values != null) {
-            subs.add(new VectorValuesSub(mergeState.docMaps[i], values));
+            subs.add(newSub.apply(docMaps[i], values));
           }
         }
       }
-      return new MergedFloat32VectorValues(subs, mergeState);
+      return subs;
+    }
+
+    /** Returns a merged view over all the segment's {@link FloatVectorValues}. */
+    public static FloatVectorValues mergeFloatVectorValues(
+        FieldInfo fieldInfo, MergeState mergeState) throws IOException {
+      validateFieldEncoding(fieldInfo, VectorEncoding.FLOAT32);
+      return new MergedFloat32VectorValues(
+          mergeVectorValues(
+              mergeState.knnVectorsReaders,
+              mergeState.docMaps,
+              knnVectorsReader -> {
+                return knnVectorsReader.getFloatVectorValues(fieldInfo.name);
+              },
+              (docMap, values) -> {
+                return new FloatVectorValuesSub(docMap, values);
+              }),
+          mergeState);
     }
 
     /** Returns a merged view over all the segment's {@link ByteVectorValues}. */
     public static ByteVectorValues mergeByteVectorValues(FieldInfo fieldInfo, MergeState mergeState)
         throws IOException {
-      assert fieldInfo != null && fieldInfo.hasVectorValues();
-      if (fieldInfo.getVectorEncoding() != VectorEncoding.BYTE) {
-        throw new UnsupportedOperationException(
-            "Cannot merge vectors encoded as [" + fieldInfo.getVectorEncoding() + "] as BYTE");
-      }
-      List<ByteVectorValuesSub> subs = new ArrayList<>();
-      for (int i = 0; i < mergeState.knnVectorsReaders.length; i++) {
-        KnnVectorsReader knnVectorsReader = mergeState.knnVectorsReaders[i];
-        if (knnVectorsReader != null) {
-          ByteVectorValues values = knnVectorsReader.getByteVectorValues(fieldInfo.name);
-          if (values != null) {
-            subs.add(new ByteVectorValuesSub(mergeState.docMaps[i], values));
-          }
-        }
-      }
-      return new MergedByteVectorValues(subs, mergeState);
+      validateFieldEncoding(fieldInfo, VectorEncoding.BYTE);
+      return new MergedByteVectorValues(
+          mergeVectorValues(
+              mergeState.knnVectorsReaders,
+              mergeState.docMaps,
+              knnVectorsReader -> {
+                return knnVectorsReader.getByteVectorValues(fieldInfo.name);
+              },
+              (docMap, values) -> {
+                return new ByteVectorValuesSub(docMap, values);
+              }),
+          mergeState);
     }
 
     static class MergedFloat32VectorValues extends FloatVectorValues {
-      private final List<VectorValuesSub> subs;
-      private final DocIDMerger<VectorValuesSub> docIdMerger;
+      private final List<FloatVectorValuesSub> subs;
+      private final DocIDMerger<FloatVectorValuesSub> docIdMerger;
       private final int size;
       private int docId;
-      VectorValuesSub current;
+      FloatVectorValuesSub current;
 
-      private MergedFloat32VectorValues(List<VectorValuesSub> subs, MergeState mergeState)
+      private MergedFloat32VectorValues(List<FloatVectorValuesSub> subs, MergeState mergeState)
           throws IOException {
         this.subs = subs;
         docIdMerger = DocIDMerger.of(subs, mergeState.needsIndexSort);
         int totalSize = 0;
-        for (VectorValuesSub sub : subs) {
+        for (FloatVectorValuesSub sub : subs) {
           totalSize += sub.values.size();
         }
         size = totalSize;

lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90DocValuesConsumer.java

@@ -19,9 +19,13 @@ package org.apache.lucene.codecs.lucene90;
 import static org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat.DIRECT_MONOTONIC_BLOCK_SHIFT;
 import static org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat.NUMERIC_BLOCK_SHIFT;
 import static org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat.NUMERIC_BLOCK_SIZE;
+import static org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat.SKIP_INDEX_LEVEL_SHIFT;
+import static org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat.SKIP_INDEX_MAX_LEVEL;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.List;
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.codecs.DocValuesConsumer;
 import org.apache.lucene.codecs.DocValuesProducer;
@@ -43,7 +47,6 @@ import org.apache.lucene.search.SortedSetSelector;
 import org.apache.lucene.store.ByteArrayDataOutput;
 import org.apache.lucene.store.ByteBuffersDataOutput;
 import org.apache.lucene.store.ByteBuffersIndexOutput;
-import org.apache.lucene.store.DataOutput;
 import org.apache.lucene.store.IndexOutput;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
@@ -202,70 +205,150 @@ final class Lucene90DocValuesConsumer extends DocValuesConsumer {
       docCount = 0;
     }
 
+    boolean isDone(int skipIndexIntervalSize, int valueCount, long nextValue, int nextDoc) {
+      if (docCount < skipIndexIntervalSize) {
+        return false;
+      }
+      // Once we reach the interval size, we will keep accepting documents if
+      // - next doc value is not a multi-value
+      // - current accumulator only contains a single value and next value is the same value
+      // - the accumulator is dense and the next doc keeps the density (no gaps)
+      return valueCount > 1
+          || minValue != maxValue
+          || minValue != nextValue
+          || docCount != nextDoc - minDocID;
+    }
+
     void accumulate(long value) {
       minValue = Math.min(minValue, value);
       maxValue = Math.max(maxValue, value);
     }
 
+    void accumulate(SkipAccumulator other) {
+      assert minDocID <= other.minDocID && maxDocID < other.maxDocID;
+      maxDocID = other.maxDocID;
+      minValue = Math.min(minValue, other.minValue);
+      maxValue = Math.max(maxValue, other.maxValue);
+      docCount += other.docCount;
+    }
+
     void nextDoc(int docID) {
       maxDocID = docID;
       ++docCount;
     }
 
-    void writeTo(DataOutput output) throws IOException {
-      output.writeInt(maxDocID);
-      output.writeInt(minDocID);
-      output.writeLong(maxValue);
-      output.writeLong(minValue);
-      output.writeInt(docCount);
+    public static SkipAccumulator merge(List<SkipAccumulator> list, int index, int length) {
+      SkipAccumulator acc = new SkipAccumulator(list.get(index).minDocID);
+      for (int i = 0; i < length; i++) {
+        acc.accumulate(list.get(index + i));
+      }
+      return acc;
     }
   }
 
   private void writeSkipIndex(FieldInfo field, DocValuesProducer valuesProducer)
       throws IOException {
     assert field.hasDocValuesSkipIndex();
-    // TODO: This disk compression once we introduce levels
-    long start = data.getFilePointer();
-    SortedNumericDocValues values = valuesProducer.getSortedNumeric(field);
+    final long start = data.getFilePointer();
+    final SortedNumericDocValues values = valuesProducer.getSortedNumeric(field);
     long globalMaxValue = Long.MIN_VALUE;
     long globalMinValue = Long.MAX_VALUE;
     int globalDocCount = 0;
     int maxDocId = -1;
+    final List<SkipAccumulator> accumulators = new ArrayList<>();
     SkipAccumulator accumulator = null;
-    int counter = 0;
+    final int maxAccumulators = 1 << (SKIP_INDEX_LEVEL_SHIFT * (SKIP_INDEX_MAX_LEVEL - 1));
     for (int doc = values.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = values.nextDoc()) {
-      if (counter == 0) {
-        accumulator = new SkipAccumulator(doc);
-      }
-      accumulator.nextDoc(doc);
-      for (int i = 0, end = values.docValueCount(); i < end; ++i) {
-        accumulator.accumulate(values.nextValue());
-      }
-      if (++counter == skipIndexIntervalSize) {
+      final long firstValue = values.nextValue();
+      if (accumulator != null
+          && accumulator.isDone(skipIndexIntervalSize, values.docValueCount(), firstValue, doc)) {
         globalMaxValue = Math.max(globalMaxValue, accumulator.maxValue);
         globalMinValue = Math.min(globalMinValue, accumulator.minValue);
         globalDocCount += accumulator.docCount;
         maxDocId = accumulator.maxDocID;
-        accumulator.writeTo(data);
-        counter = 0;
+        accumulator = null;
+        if (accumulators.size() == maxAccumulators) {
+          writeLevels(accumulators);
+          accumulators.clear();
+        }
+      }
+      if (accumulator == null) {
+        accumulator = new SkipAccumulator(doc);
+        accumulators.add(accumulator);
+      }
+      accumulator.nextDoc(doc);
+      accumulator.accumulate(firstValue);
+      for (int i = 1, end = values.docValueCount(); i < end; ++i) {
+        accumulator.accumulate(values.nextValue());
       }
     }
 
-    if (counter > 0) {
+    if (accumulators.isEmpty() == false) {
       globalMaxValue = Math.max(globalMaxValue, accumulator.maxValue);
       globalMinValue = Math.min(globalMinValue, accumulator.minValue);
       globalDocCount += accumulator.docCount;
       maxDocId = accumulator.maxDocID;
-      accumulator.writeTo(data);
+      writeLevels(accumulators);
     }
     meta.writeLong(start); // record the start in meta
     meta.writeLong(data.getFilePointer() - start); // record the length
+    assert globalDocCount == 0 || globalMaxValue >= globalMinValue;
     meta.writeLong(globalMaxValue);
     meta.writeLong(globalMinValue);
+    assert globalDocCount <= maxDocId + 1;
     meta.writeInt(globalDocCount);
     meta.writeInt(maxDocId);
   }
 
+  private void writeLevels(List<SkipAccumulator> accumulators) throws IOException {
+    final List<List<SkipAccumulator>> accumulatorsLevels = new ArrayList<>(SKIP_INDEX_MAX_LEVEL);
+    accumulatorsLevels.add(accumulators);
+    for (int i = 0; i < SKIP_INDEX_MAX_LEVEL - 1; i++) {
+      accumulatorsLevels.add(buildLevel(accumulatorsLevels.get(i)));
+    }
+    int totalAccumulators = accumulators.size();
+    for (int index = 0; index < totalAccumulators; index++) {
+      // compute how many levels we need to write for the current accumulator
+      final int levels = getLevels(index, totalAccumulators);
+      // write the number of levels
+      data.writeByte((byte) levels);
+      // write intervals in reverse order. This is done so we don't
+      // need to read all of them in case of slipping
+      for (int level = levels - 1; level >= 0; level--) {
+        final SkipAccumulator accumulator =
+            accumulatorsLevels.get(level).get(index >> (SKIP_INDEX_LEVEL_SHIFT * level));
+        data.writeInt(accumulator.maxDocID);
+        data.writeInt(accumulator.minDocID);
+        data.writeLong(accumulator.maxValue);
+        data.writeLong(accumulator.minValue);
+        data.writeInt(accumulator.docCount);
+      }
+    }
+  }
+
+  private static List<SkipAccumulator> buildLevel(List<SkipAccumulator> accumulators) {
+    final int levelSize = 1 << SKIP_INDEX_LEVEL_SHIFT;
+    final List<SkipAccumulator> collector = new ArrayList<>();
+    for (int i = 0; i < accumulators.size() - levelSize + 1; i += levelSize) {
+      collector.add(SkipAccumulator.merge(accumulators, i, levelSize));
+    }
+    return collector;
+  }
+
+  private static int getLevels(int index, int size) {
+    if (Integer.numberOfTrailingZeros(index) >= SKIP_INDEX_LEVEL_SHIFT) {
+      // TODO: can we do it in constant time rather than linearly with SKIP_INDEX_MAX_LEVEL?
+      final int left = size - index;
+      for (int level = SKIP_INDEX_MAX_LEVEL - 1; level > 0; level--) {
+        final int numberIntervals = 1 << (SKIP_INDEX_LEVEL_SHIFT * level);
+        if (left >= numberIntervals && index % numberIntervals == 0) {
+          return level + 1;
+        }
+      }
+    }
+    return 1;
+  }
+
   private long[] writeValues(FieldInfo field, DocValuesProducer valuesProducer, boolean ords)
       throws IOException {
     SortedNumericDocValues values = valuesProducer.getSortedNumeric(field);

lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90DocValuesFormat.java

@@ -194,5 +194,36 @@ public final class Lucene90DocValuesFormat extends DocValuesFormat {
   static final int TERMS_DICT_REVERSE_INDEX_SIZE = 1 << TERMS_DICT_REVERSE_INDEX_SHIFT;
   static final int TERMS_DICT_REVERSE_INDEX_MASK = TERMS_DICT_REVERSE_INDEX_SIZE - 1;
 
+  // number of documents in an interval
   private static final int DEFAULT_SKIP_INDEX_INTERVAL_SIZE = 4096;
+  // bytes on an interval:
+  //   * 1 byte : number of levels
+  //   * 16 bytes: min / max value,
+  //   * 8 bytes:  min / max docID
+  //   * 4 bytes: number of documents
+  private static final long SKIP_INDEX_INTERVAL_BYTES = 29L;
+  // number of intervals represented as a shift to create a new level, this is 1 << 3 == 8
+  // intervals.
+  static final int SKIP_INDEX_LEVEL_SHIFT = 3;
+  // max number of levels
+  // Increasing this number, it increases how much heap we need at index time.
+  // we currently need (1 * 8 * 8 * 8)  = 512 accumulators on heap
+  static final int SKIP_INDEX_MAX_LEVEL = 4;
+  // number of bytes to skip when skipping a level. It does not take into account the
+  // current interval that is being read.
+  static final long[] SKIP_INDEX_JUMP_LENGTH_PER_LEVEL = new long[SKIP_INDEX_MAX_LEVEL];
+
+  static {
+    // Size of the interval minus read bytes (1 byte for level and 4 bytes for maxDocID)
+    SKIP_INDEX_JUMP_LENGTH_PER_LEVEL[0] = SKIP_INDEX_INTERVAL_BYTES - 5L;
+    for (int level = 1; level < SKIP_INDEX_MAX_LEVEL; level++) {
+      // jump from previous level
+      SKIP_INDEX_JUMP_LENGTH_PER_LEVEL[level] = SKIP_INDEX_JUMP_LENGTH_PER_LEVEL[level - 1];
+      // nodes added by new level
+      SKIP_INDEX_JUMP_LENGTH_PER_LEVEL[level] +=
+          (1 << (level * SKIP_INDEX_LEVEL_SHIFT)) * SKIP_INDEX_INTERVAL_BYTES;
+      // remove the byte levels added in the previous level
+      SKIP_INDEX_JUMP_LENGTH_PER_LEVEL[level] -= (1 << ((level - 1) * SKIP_INDEX_LEVEL_SHIFT));
+    }
+  }
 }

lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90DocValuesProducer.java

@@ -16,6 +16,8 @@
  */
 package org.apache.lucene.codecs.lucene90;
 
+import static org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat.SKIP_INDEX_JUMP_LENGTH_PER_LEVEL;
+import static org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat.SKIP_INDEX_MAX_LEVEL;
 import static org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat.TERMS_DICT_BLOCK_LZ4_SHIFT;
 
 import java.io.IOException;
@@ -1792,28 +1794,55 @@ final class Lucene90DocValuesProducer extends DocValuesProducer {
     if (input.length() > 0) {
       input.prefetch(0, 1);
     }
+    // TODO: should we write to disk the actual max level for this segment?
     return new DocValuesSkipper() {
-      int minDocID = -1;
-      int maxDocID = -1;
-      long minValue, maxValue;
-      int docCount;
+      final int[] minDocID = new int[SKIP_INDEX_MAX_LEVEL];
+      final int[] maxDocID = new int[SKIP_INDEX_MAX_LEVEL];
+
+      {
+        for (int i = 0; i < SKIP_INDEX_MAX_LEVEL; i++) {
+          minDocID[i] = maxDocID[i] = -1;
+        }
+      }
+
+      final long[] minValue = new long[SKIP_INDEX_MAX_LEVEL];
+      final long[] maxValue = new long[SKIP_INDEX_MAX_LEVEL];
+      final int[] docCount = new int[SKIP_INDEX_MAX_LEVEL];
+      int levels = 1;
 
       @Override
       public void advance(int target) throws IOException {
         if (target > entry.maxDocId) {
-          minDocID = DocIdSetIterator.NO_MORE_DOCS;
-          maxDocID = DocIdSetIterator.NO_MORE_DOCS;
+          // skipper is exhausted
+          for (int i = 0; i < SKIP_INDEX_MAX_LEVEL; i++) {
+            minDocID[i] = maxDocID[i] = DocIdSetIterator.NO_MORE_DOCS;
+          }
         } else {
+          // find next interval
+          assert target > maxDocID[0] : "target must be bigger that current interval";
           while (true) {
-            maxDocID = input.readInt();
-            if (maxDocID >= target) {
-              minDocID = input.readInt();
-              maxValue = input.readLong();
-              minValue = input.readLong();
-              docCount = input.readInt();
+            levels = input.readByte();
+            assert levels <= SKIP_INDEX_MAX_LEVEL && levels > 0
+                : "level out of range [" + levels + "]";
+            boolean valid = true;
+            // check if current interval is competitive or we can jump to the next position
+            for (int level = levels - 1; level >= 0; level--) {
+              if ((maxDocID[level] = input.readInt()) < target) {
+                input.skipBytes(SKIP_INDEX_JUMP_LENGTH_PER_LEVEL[level]); // the jump for the level
+                valid = false;
+                break;
+              }
+              minDocID[level] = input.readInt();
+              maxValue[level] = input.readLong();
+              minValue[level] = input.readLong();
+              docCount[level] = input.readInt();
+            }
+            if (valid) {
+              // adjust levels
+              while (levels < SKIP_INDEX_MAX_LEVEL && maxDocID[levels] >= target) {
+                levels++;
+              }
               break;
-            } else {
-              input.skipBytes(24);
             }
           }
         }
@@ -1821,32 +1850,32 @@ final class Lucene90DocValuesProducer extends DocValuesProducer {
 
       @Override
       public int numLevels() {
-        return 1;
+        return levels;
       }
 
       @Override
       public int minDocID(int level) {
-        return minDocID;
+        return minDocID[level];
       }
 
       @Override
       public int maxDocID(int level) {
-        return maxDocID;
+        return maxDocID[level];
       }
 
       @Override
       public long minValue(int level) {
-        return minValue;
+        return minValue[level];
       }
 
       @Override
       public long maxValue(int level) {
-        return maxValue;
+        return maxValue[level];
       }
 
       @Override
       public int docCount(int level) {
-        return docCount;
+        return docCount[level];
       }
 
       @Override

lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90StoredFieldsFormat.java

@@ -49,9 +49,9 @@ import org.apache.lucene.util.packed.DirectMonotonicWriter;
  *
  * <pre class="prettyprint">
  *   // the default: for high performance
- *   indexWriterConfig.setCodec(new Lucene99Codec(Mode.BEST_SPEED));
+ *   indexWriterConfig.setCodec(new Lucene912Codec(Mode.BEST_SPEED));
  *   // instead for higher performance (but slower):
- *   // indexWriterConfig.setCodec(new Lucene99Codec(Mode.BEST_COMPRESSION));
+ *   // indexWriterConfig.setCodec(new Lucene912Codec(Mode.BEST_COMPRESSION));
  * </pre>
  *
  * <p><b>File formats</b>

lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/FieldReader.java

@@ -78,7 +78,6 @@ public final class FieldReader extends Terms {
     this.sumTotalTermFreq = sumTotalTermFreq;
     this.sumDocFreq = sumDocFreq;
     this.docCount = docCount;
-    this.rootCode = rootCode;
     this.minTerm = minTerm;
     this.maxTerm = maxTerm;
     // if (DEBUG) {
@@ -100,6 +99,14 @@ public final class FieldReader extends Terms {
      w.close();
      }
     */
+    BytesRef emptyOutput = metadata.getEmptyOutput();
+    if (rootCode.equals(emptyOutput) == false) {
+      // TODO: this branch is never taken
+      assert false;
+      this.rootCode = rootCode;
+    } else {
+      this.rootCode = emptyOutput;
+    }
   }
 
   long readVLongOutput(DataInput in) throws IOException {

lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/Lucene90BlockTreeTermsReader.java

@@ -200,6 +200,11 @@ public final class Lucene90BlockTreeTermsReader extends FieldsProducer {
             final int docCount = metaIn.readVInt();
             BytesRef minTerm = readBytesRef(metaIn);
             BytesRef maxTerm = readBytesRef(metaIn);
+            if (numTerms == 1) {
+              assert maxTerm.equals(minTerm);
+              // save heap for edge case of a single term only so min == max
+              maxTerm = minTerm;
+            }
             if (docCount < 0
                 || docCount > state.segmentInfo.maxDoc()) { // #docs with field must be <= #docs
               throw new CorruptIndexException(
@@ -270,9 +275,8 @@ public final class Lucene90BlockTreeTermsReader extends FieldsProducer {
       throw new CorruptIndexException("invalid bytes length: " + numBytes, in);
     }
 
-    BytesRef bytes = new BytesRef();
+    BytesRef bytes = new BytesRef(numBytes);
     bytes.length = numBytes;
-    bytes.bytes = new byte[numBytes];
     in.readBytes(bytes.bytes, 0, numBytes);
 
     return bytes;

lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/Lucene90BlockTreeTermsWriter.java

@@ -598,8 +598,6 @@ public final class Lucene90BlockTreeTermsWriter extends FieldsConsumer {
   private final ByteBuffersDataOutput scratchBytes = ByteBuffersDataOutput.newResettableInstance();
   private final IntsRefBuilder scratchIntsRef = new IntsRefBuilder();
 
-  static final BytesRef EMPTY_BYTES_REF = new BytesRef();
-
   private static class StatsWriter {
 
     private final DataOutput out;

lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/SegmentTermsEnum.java

@@ -277,10 +277,10 @@ final class SegmentTermsEnum extends BaseTermsEnum {
         //   System.out.println("        skip rewind!");
         // }
       }
-      assert length == f.prefix;
+      assert length == f.prefixLength;
     } else {
       f.nextEnt = -1;
-      f.prefix = length;
+      f.prefixLength = length;
       f.state.termBlockOrd = 0;
       f.fpOrig = f.fp = fp;
       f.lastSubFP = -1;
@@ -488,7 +488,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
         // toHex(targetLabel));
         // }
 
-        validIndexPrefix = currentFrame.prefix;
+        validIndexPrefix = currentFrame.prefixLength;
         // validIndexPrefix = targetUpto;
 
         currentFrame.scanToFloorFrame(target);
@@ -550,7 +550,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
     }
 
     // validIndexPrefix = targetUpto;
-    validIndexPrefix = currentFrame.prefix;
+    validIndexPrefix = currentFrame.prefixLength;
 
     currentFrame.scanToFloorFrame(target);
 
@@ -772,7 +772,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
         // targetLabel);
         // }
 
-        validIndexPrefix = currentFrame.prefix;
+        validIndexPrefix = currentFrame.prefixLength;
         // validIndexPrefix = targetUpto;
 
         currentFrame.scanToFloorFrame(target);
@@ -830,7 +830,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
     }
 
     // validIndexPrefix = targetUpto;
-    validIndexPrefix = currentFrame.prefix;
+    validIndexPrefix = currentFrame.prefixLength;
 
     currentFrame.scanToFloorFrame(target);
 
@@ -868,7 +868,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
       while (true) {
         SegmentTermsEnumFrame f = getFrame(ord);
         assert f != null;
-        final BytesRef prefix = new BytesRef(term.get().bytes, 0, f.prefix);
+        final BytesRef prefix = new BytesRef(term.get().bytes, 0, f.prefixLength);
         if (f.nextEnt == -1) {
           out.println(
               "    frame "
@@ -879,7 +879,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
                   + f.fp
                   + (f.isFloor ? (" (fpOrig=" + f.fpOrig + ")") : "")
                   + " prefixLen="
-                  + f.prefix
+                  + f.prefixLength
                   + " prefix="
                   + prefix
                   + (f.nextEnt == -1 ? "" : (" (of " + f.entCount + ")"))
@@ -907,7 +907,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
                   + f.fp
                   + (f.isFloor ? (" (fpOrig=" + f.fpOrig + ")") : "")
                   + " prefixLen="
-                  + f.prefix
+                  + f.prefixLength
                   + " prefix="
                   + prefix
                   + " nextEnt="
@@ -932,12 +932,14 @@ final class SegmentTermsEnum extends BaseTermsEnum {
         }
         if (fr.index != null) {
           assert !isSeekFrame || f.arc != null : "isSeekFrame=" + isSeekFrame + " f.arc=" + f.arc;
-          if (f.prefix > 0 && isSeekFrame && f.arc.label() != (term.byteAt(f.prefix - 1) & 0xFF)) {
+          if (f.prefixLength > 0
+              && isSeekFrame
+              && f.arc.label() != (term.byteAt(f.prefixLength - 1) & 0xFF)) {
             out.println(
                 "      broken seek state: arc.label="
                     + (char) f.arc.label()
                     + " vs term byte="
-                    + (char) (term.byteAt(f.prefix - 1) & 0xFF));
+                    + (char) (term.byteAt(f.prefixLength - 1) & 0xFF));
             throw new RuntimeException("seek state is broken");
           }
           BytesRef output = Util.get(fr.index, prefix);
@@ -965,7 +967,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
         if (f == currentFrame) {
           break;
         }
-        if (f.prefix == validIndexPrefix) {
+        if (f.prefixLength == validIndexPrefix) {
           isSeekFrame = false;
         }
         ord++;
@@ -1046,7 +1048,7 @@ final class SegmentTermsEnum extends BaseTermsEnum {
 
         // Note that the seek state (last seek) has been
         // invalidated beyond this depth
-        validIndexPrefix = Math.min(validIndexPrefix, currentFrame.prefix);
+        validIndexPrefix = Math.min(validIndexPrefix, currentFrame.prefixLength);
         // if (DEBUG) {
         // System.out.println("  reset validIndexPrefix=" + validIndexPrefix);
         // }

lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/SegmentTermsEnumFrame.java

@@ -59,7 +59,7 @@ final class SegmentTermsEnumFrame {
   final ByteArrayDataInput floorDataReader = new ByteArrayDataInput();
 
   // Length of prefix shared by all terms in this block
-  int prefix;
+  int prefixLength;
 
   // Number of entries (term or sub-block) in this block
   int entCount;
@@ -318,11 +318,11 @@ final class SegmentTermsEnumFrame {
     assert nextEnt != -1 && nextEnt < entCount
         : "nextEnt=" + nextEnt + " entCount=" + entCount + " fp=" + fp;
     nextEnt++;
-    suffix = suffixLengthsReader.readVInt();
+    suffixLength = suffixLengthsReader.readVInt();
     startBytePos = suffixesReader.getPosition();
-    ste.term.setLength(prefix + suffix);
+    ste.term.setLength(prefixLength + suffixLength);
     ste.term.grow(ste.term.length());
-    suffixesReader.readBytes(ste.term.bytes(), prefix, suffix);
+    suffixesReader.readBytes(ste.term.bytes(), prefixLength, suffixLength);
     ste.termExists = true;
   }
 
@@ -346,11 +346,11 @@ final class SegmentTermsEnumFrame {
           : "nextEnt=" + nextEnt + " entCount=" + entCount + " fp=" + fp;
       nextEnt++;
       final int code = suffixLengthsReader.readVInt();
-      suffix = code >>> 1;
+      suffixLength = code >>> 1;
       startBytePos = suffixesReader.getPosition();
-      ste.term.setLength(prefix + suffix);
+      ste.term.setLength(prefixLength + suffixLength);
       ste.term.grow(ste.term.length());
-      suffixesReader.readBytes(ste.term.bytes(), prefix, suffix);
+      suffixesReader.readBytes(ste.term.bytes(), prefixLength, suffixLength);
       if ((code & 1) == 0) {
         // A normal term
         ste.termExists = true;
@@ -375,7 +375,7 @@ final class SegmentTermsEnumFrame {
   // floor blocks we "typically" get
   public void scanToFloorFrame(BytesRef target) {
 
-    if (!isFloor || target.length <= prefix) {
+    if (!isFloor || target.length <= prefixLength) {
       // if (DEBUG) {
       //   System.out.println("    scanToFloorFrame skip: isFloor=" + isFloor + " target.length=" +
       // target.length + " vs prefix=" + prefix);
@@ -383,7 +383,7 @@ final class SegmentTermsEnumFrame {
       return;
     }
 
-    final int targetLabel = target.bytes[target.offset + prefix] & 0xFF;
+    final int targetLabel = target.bytes[target.offset + prefixLength] & 0xFF;
 
     // if (DEBUG) {
     //   System.out.println("    scanToFloorFrame fpOrig=" + fpOrig + " targetLabel=" +
@@ -497,7 +497,7 @@ final class SegmentTermsEnumFrame {
 
   // Used only by assert
   private boolean prefixMatches(BytesRef target) {
-    for (int bytePos = 0; bytePos < prefix; bytePos++) {
+    for (int bytePos = 0; bytePos < prefixLength; bytePos++) {
       if (target.bytes[target.offset + bytePos] != ste.term.byteAt(bytePos)) {
         return false;
       }
@@ -553,7 +553,7 @@ final class SegmentTermsEnumFrame {
   }
 
   private int startBytePos;
-  private int suffix;
+  private int suffixLength;
   private long subCode;
   CompressionAlgorithm compressionAlg = CompressionAlgorithm.NO_COMPRESSION;
 
@@ -584,7 +584,7 @@ final class SegmentTermsEnumFrame {
     do {
       nextEnt++;
 
-      suffix = suffixLengthsReader.readVInt();
+      suffixLength = suffixLengthsReader.readVInt();
 
       // if (DEBUG) {
       //   BytesRef suffixBytesRef = new BytesRef();
@@ -596,16 +596,16 @@ final class SegmentTermsEnumFrame {
       // }
 
       startBytePos = suffixesReader.getPosition();
-      suffixesReader.skipBytes(suffix);
+      suffixesReader.skipBytes(suffixLength);
 
       // Loop over bytes in the suffix, comparing to the target
       final int cmp =
           Arrays.compareUnsigned(
               suffixBytes,
               startBytePos,
-              startBytePos + suffix,
+              startBytePos + suffixLength,
               target.bytes,
-              target.offset + prefix,
+              target.offset + prefixLength,
               target.offset + target.length);
 
       if (cmp < 0) {
@@ -674,7 +674,7 @@ final class SegmentTermsEnumFrame {
 
     assert prefixMatches(target);
 
-    suffix = suffixLengthsReader.readVInt();
+    suffixLength = suffixLengthsReader.readVInt();
     // TODO early terminate when target length unequals suffix + prefix.
     // But we need to keep the same status with scanToTermLeaf.
     int start = nextEnt;
@@ -684,16 +684,16 @@ final class SegmentTermsEnumFrame {
     while (start <= end) {
       int mid = (start + end) >>> 1;
       nextEnt = mid + 1;
-      startBytePos = mid * suffix;
+      startBytePos = mid * suffixLength;
 
       // Binary search bytes in the suffix, comparing to the target.
       cmp =
           Arrays.compareUnsigned(
               suffixBytes,
               startBytePos,
-              startBytePos + suffix,
+              startBytePos + suffixLength,
               target.bytes,
-              target.offset + prefix,
+              target.offset + prefixLength,
               target.offset + target.length);
       if (cmp < 0) {
         start = mid + 1;
@@ -701,7 +701,7 @@ final class SegmentTermsEnumFrame {
         end = mid - 1;
       } else {
         // Exact match!
-        suffixesReader.setPosition(startBytePos + suffix);
+        suffixesReader.setPosition(startBytePos + suffixLength);
         fillTerm();
         // if (DEBUG) System.out.println("        found!");
         return SeekStatus.FOUND;
@@ -724,14 +724,14 @@ final class SegmentTermsEnumFrame {
       // If binary search ended at the less term, and greater term exists.
       // We need to advance to the greater term.
       if (cmp < 0) {
-        startBytePos += suffix;
+        startBytePos += suffixLength;
         nextEnt++;
       }
-      suffixesReader.setPosition(startBytePos + suffix);
+      suffixesReader.setPosition(startBytePos + suffixLength);
       fillTerm();
     } else {
       seekStatus = SeekStatus.END;
-      suffixesReader.setPosition(startBytePos + suffix);
+      suffixesReader.setPosition(startBytePos + suffixLength);
       if (exactOnly) {
         fillTerm();
       }
@@ -769,7 +769,7 @@ final class SegmentTermsEnumFrame {
       nextEnt++;
 
       final int code = suffixLengthsReader.readVInt();
-      suffix = code >>> 1;
+      suffixLength = code >>> 1;
 
       // if (DEBUG) {
       //  BytesRef suffixBytesRef = new BytesRef();
@@ -782,7 +782,7 @@ final class SegmentTermsEnumFrame {
       // }
 
       startBytePos = suffixesReader.getPosition();
-      suffixesReader.skipBytes(suffix);
+      suffixesReader.skipBytes(suffixLength);
       ste.termExists = (code & 1) == 0;
       if (ste.termExists) {
         state.termBlockOrd++;
@@ -796,9 +796,9 @@ final class SegmentTermsEnumFrame {
           Arrays.compareUnsigned(
               suffixBytes,
               startBytePos,
-              startBytePos + suffix,
+              startBytePos + suffixLength,
               target.bytes,
-              target.offset + prefix,
+              target.offset + prefixLength,
               target.offset + target.length);
 
       if (cmp < 0) {
@@ -819,7 +819,8 @@ final class SegmentTermsEnumFrame {
           // us to position to the next term after
           // the target, so we must recurse into the
           // sub-frame(s):
-          ste.currentFrame = ste.pushFrame(null, ste.currentFrame.lastSubFP, prefix + suffix);
+          ste.currentFrame =
+              ste.pushFrame(null, ste.currentFrame.lastSubFP, prefixLength + suffixLength);
           ste.currentFrame.loadBlock();
           while (ste.currentFrame.next()) {
             ste.currentFrame = ste.pushFrame(null, ste.currentFrame.lastSubFP, ste.term.length());
@@ -864,9 +865,9 @@ final class SegmentTermsEnumFrame {
   }
 
   private void fillTerm() {
-    final int termLength = prefix + suffix;
+    final int termLength = prefixLength + suffixLength;
     ste.term.setLength(termLength);
     ste.term.grow(termLength);
-    System.arraycopy(suffixBytes, startBytePos, ste.term.bytes(), prefix, suffix);
+    System.arraycopy(suffixBytes, startBytePos, ste.term.bytes(), prefixLength, suffixLength);
   }
 }

lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/Stats.java

@@ -116,10 +116,10 @@ public class Stats {
       nonFloorBlockCount++;
     }
 
-    if (blockCountByPrefixLen.length <= frame.prefix) {
-      blockCountByPrefixLen = ArrayUtil.grow(blockCountByPrefixLen, 1 + frame.prefix);
+    if (blockCountByPrefixLen.length <= frame.prefixLength) {
+      blockCountByPrefixLen = ArrayUtil.grow(blockCountByPrefixLen, 1 + frame.prefixLength);
     }
-    blockCountByPrefixLen[frame.prefix]++;
+    blockCountByPrefixLen[frame.prefixLength]++;
     startBlockCount++;
     totalBlockSuffixBytes += frame.totalSuffixBytes;
     totalUncompressedBlockSuffixBytes += frame.suffixesReader.length();

lucene/core/src/java/org/apache/lucene/codecs/lucene912/ForDeltaUtil.java

@@ -0,0 +1,83 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene912;
+
+import java.io.IOException;
+import org.apache.lucene.store.DataInput;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.packed.PackedInts;
+
+/** Utility class to encode/decode increasing sequences of 128 integers. */
+final class ForDeltaUtil {
+
+  // IDENTITY_PLUS_ONE[i] == i+1
+  private static final long[] IDENTITY_PLUS_ONE = new long[ForUtil.BLOCK_SIZE];
+
+  static {
+    for (int i = 0; i < ForUtil.BLOCK_SIZE; ++i) {
+      IDENTITY_PLUS_ONE[i] = i + 1;
+    }
+  }
+
+  private static void prefixSumOfOnes(long[] arr, long base) {
+    System.arraycopy(IDENTITY_PLUS_ONE, 0, arr, 0, ForUtil.BLOCK_SIZE);
+    // This loop gets auto-vectorized
+    for (int i = 0; i < ForUtil.BLOCK_SIZE; ++i) {
+      arr[i] += base;
+    }
+  }
+
+  private final ForUtil forUtil;
+
+  ForDeltaUtil(ForUtil forUtil) {
+    this.forUtil = forUtil;
+  }
+
+  /**
+   * Encode deltas of a strictly monotonically increasing sequence of integers. The provided {@code
+   * longs} are expected to be deltas between consecutive values.
+   */
+  void encodeDeltas(long[] longs, DataOutput out) throws IOException {
+    if (longs[0] == 1 && PForUtil.allEqual(longs)) { // happens with very dense postings
+      out.writeByte((byte) 0);
+    } else {
+      long or = 0;
+      for (long l : longs) {
+        or |= l;
+      }
+      assert or != 0;
+      final int bitsPerValue = PackedInts.bitsRequired(or);
+      out.writeByte((byte) bitsPerValue);
+      forUtil.encode(longs, bitsPerValue, out);
+    }
+  }
+
+  /** Decode deltas, compute the prefix sum and add {@code base} to all decoded longs. */
+  void decodeAndPrefixSum(PostingIndexInput in, long base, long[] longs) throws IOException {
+    final int bitsPerValue = Byte.toUnsignedInt(in.in.readByte());
+    if (bitsPerValue == 0) {
+      prefixSumOfOnes(longs, base);
+    } else {
+      in.decodeAndPrefixSum(bitsPerValue, base, longs);
+    }
+  }
+
+  void skip(DataInput in) throws IOException {
+    final int bitsPerValue = Byte.toUnsignedInt(in.readByte());
+    in.skipBytes(forUtil.numBytes(bitsPerValue));
+  }
+}

lucene/core/src/java/org/apache/lucene/codecs/lucene912/Lucene912Codec.java

@@ -0,0 +1,217 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene912;
+
+import java.util.Objects;
+import org.apache.lucene.codecs.Codec;
+import org.apache.lucene.codecs.CompoundFormat;
+import org.apache.lucene.codecs.DocValuesFormat;
+import org.apache.lucene.codecs.FieldInfosFormat;
+import org.apache.lucene.codecs.FilterCodec;
+import org.apache.lucene.codecs.KnnVectorsFormat;
+import org.apache.lucene.codecs.LiveDocsFormat;
+import org.apache.lucene.codecs.NormsFormat;
+import org.apache.lucene.codecs.PointsFormat;
+import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.SegmentInfoFormat;
+import org.apache.lucene.codecs.StoredFieldsFormat;
+import org.apache.lucene.codecs.TermVectorsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90CompoundFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90NormsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90PointsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat;
+import org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat;
+import org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat;
+import org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat;
+import org.apache.lucene.codecs.perfield.PerFieldDocValuesFormat;
+import org.apache.lucene.codecs.perfield.PerFieldKnnVectorsFormat;
+import org.apache.lucene.codecs.perfield.PerFieldPostingsFormat;
+
+/**
+ * Implements the Lucene 9.12 index format
+ *
+ * <p>If you want to reuse functionality of this codec in another codec, extend {@link FilterCodec}.
+ *
+ * @see org.apache.lucene.codecs.lucene99 package documentation for file format details.
+ * @lucene.experimental
+ */
+public class Lucene912Codec extends Codec {
+
+  /** Configuration option for the codec. */
+  public enum Mode {
+    /** Trade compression ratio for retrieval speed. */
+    BEST_SPEED(Lucene90StoredFieldsFormat.Mode.BEST_SPEED),
+    /** Trade retrieval speed for compression ratio. */
+    BEST_COMPRESSION(Lucene90StoredFieldsFormat.Mode.BEST_COMPRESSION);
+
+    private final Lucene90StoredFieldsFormat.Mode storedMode;
+
+    private Mode(Lucene90StoredFieldsFormat.Mode storedMode) {
+      this.storedMode = Objects.requireNonNull(storedMode);
+    }
+  }
+
+  private final TermVectorsFormat vectorsFormat = new Lucene90TermVectorsFormat();
+  private final FieldInfosFormat fieldInfosFormat = new Lucene94FieldInfosFormat();
+  private final SegmentInfoFormat segmentInfosFormat = new Lucene99SegmentInfoFormat();
+  private final LiveDocsFormat liveDocsFormat = new Lucene90LiveDocsFormat();
+  private final CompoundFormat compoundFormat = new Lucene90CompoundFormat();
+  private final NormsFormat normsFormat = new Lucene90NormsFormat();
+
+  private final PostingsFormat defaultPostingsFormat;
+  private final PostingsFormat postingsFormat =
+      new PerFieldPostingsFormat() {
+        @Override
+        public PostingsFormat getPostingsFormatForField(String field) {
+          return Lucene912Codec.this.getPostingsFormatForField(field);
+        }
+      };
+
+  private final DocValuesFormat defaultDVFormat;
+  private final DocValuesFormat docValuesFormat =
+      new PerFieldDocValuesFormat() {
+        @Override
+        public DocValuesFormat getDocValuesFormatForField(String field) {
+          return Lucene912Codec.this.getDocValuesFormatForField(field);
+        }
+      };
+
+  private final KnnVectorsFormat defaultKnnVectorsFormat;
+  private final KnnVectorsFormat knnVectorsFormat =
+      new PerFieldKnnVectorsFormat() {
+        @Override
+        public KnnVectorsFormat getKnnVectorsFormatForField(String field) {
+          return Lucene912Codec.this.getKnnVectorsFormatForField(field);
+        }
+      };
+
+  private final StoredFieldsFormat storedFieldsFormat;
+
+  /** Instantiates a new codec. */
+  public Lucene912Codec() {
+    this(Mode.BEST_SPEED);
+  }
+
+  /**
+   * Instantiates a new codec, specifying the stored fields compression mode to use.
+   *
+   * @param mode stored fields compression mode to use for newly flushed/merged segments.
+   */
+  public Lucene912Codec(Mode mode) {
+    super("Lucene912");
+    this.storedFieldsFormat =
+        new Lucene90StoredFieldsFormat(Objects.requireNonNull(mode).storedMode);
+    this.defaultPostingsFormat = new Lucene912PostingsFormat();
+    this.defaultDVFormat = new Lucene90DocValuesFormat();
+    this.defaultKnnVectorsFormat = new Lucene99HnswVectorsFormat();
+  }
+
+  @Override
+  public final StoredFieldsFormat storedFieldsFormat() {
+    return storedFieldsFormat;
+  }
+
+  @Override
+  public final TermVectorsFormat termVectorsFormat() {
+    return vectorsFormat;
+  }
+
+  @Override
+  public final PostingsFormat postingsFormat() {
+    return postingsFormat;
+  }
+
+  @Override
+  public final FieldInfosFormat fieldInfosFormat() {
+    return fieldInfosFormat;
+  }
+
+  @Override
+  public final SegmentInfoFormat segmentInfoFormat() {
+    return segmentInfosFormat;
+  }
+
+  @Override
+  public final LiveDocsFormat liveDocsFormat() {
+    return liveDocsFormat;
+  }
+
+  @Override
+  public final CompoundFormat compoundFormat() {
+    return compoundFormat;
+  }
+
+  @Override
+  public final PointsFormat pointsFormat() {
+    return new Lucene90PointsFormat();
+  }
+
+  @Override
+  public final KnnVectorsFormat knnVectorsFormat() {
+    return knnVectorsFormat;
+  }
+
+  /**
+   * Returns the postings format that should be used for writing new segments of <code>field</code>.
+   *
+   * <p>The default implementation always returns "Lucene912".
+   *
+   * <p><b>WARNING:</b> if you subclass, you are responsible for index backwards compatibility:
+   * future version of Lucene are only guaranteed to be able to read the default implementation,
+   */
+  public PostingsFormat getPostingsFormatForField(String field) {
+    return defaultPostingsFormat;
+  }
+
+  /**
+   * Returns the docvalues format that should be used for writing new segments of <code>field</code>
+   * .
+   *
+   * <p>The default implementation always returns "Lucene90".
+   *
+   * <p><b>WARNING:</b> if you subclass, you are responsible for index backwards compatibility:
+   * future version of Lucene are only guaranteed to be able to read the default implementation.
+   */
+  public DocValuesFormat getDocValuesFormatForField(String field) {
+    return defaultDVFormat;
+  }
+
+  /**
+   * Returns the vectors format that should be used for writing new segments of <code>field</code>
+   *
+   * <p>The default implementation always returns "Lucene99HnswVectorsFormat".
+   *
+   * <p><b>WARNING:</b> if you subclass, you are responsible for index backwards compatibility:
+   * future version of Lucene are only guaranteed to be able to read the default implementation.
+   */
+  public KnnVectorsFormat getKnnVectorsFormatForField(String field) {
+    return defaultKnnVectorsFormat;
+  }
+
+  @Override
+  public final DocValuesFormat docValuesFormat() {
+    return docValuesFormat;
+  }
+
+  @Override
+  public final NormsFormat normsFormat() {
+    return normsFormat;
+  }
+}

lucene/core/src/java/org/apache/lucene/codecs/lucene912/Lucene912PostingsFormat.java

@@ -0,0 +1,492 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene912;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.FieldsConsumer;
+import org.apache.lucene.codecs.FieldsProducer;
+import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.PostingsReaderBase;
+import org.apache.lucene.codecs.PostingsWriterBase;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsReader;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
+import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
+import org.apache.lucene.index.TermState;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.packed.PackedInts;
+
+/**
+ * Lucene 9.12 postings format, which encodes postings in packed integer blocks for fast decode.
+ *
+ * <p>Basic idea:
+ *
+ * <ul>
+ *   <li><b>Packed Blocks and VInt Blocks</b>:
+ *       <p>In packed blocks, integers are encoded with the same bit width ({@link PackedInts packed
+ *       format}): the block size (i.e. number of integers inside block) is fixed (currently 128).
+ *       Additionally blocks that are all the same value are encoded in an optimized way.
+ *       <p>In VInt blocks, integers are encoded as {@link DataOutput#writeVInt VInt}: the block
+ *       size is variable.
+ *   <li><b>Block structure</b>:
+ *       <p>When the postings are long enough, Lucene912PostingsFormat will try to encode most
+ *       integer data as a packed block.
+ *       <p>Take a term with 259 documents as an example, the first 256 document ids are encoded as
+ *       two packed blocks, while the remaining 3 are encoded as one VInt block.
+ *       <p>Different kinds of data are always encoded separately into different packed blocks, but
+ *       may possibly be interleaved into the same VInt block.
+ *       <p>This strategy is applied to pairs: &lt;document number, frequency&gt;, &lt;position,
+ *       payload length&gt;, &lt;position, offset start, offset length&gt;, and &lt;position,
+ *       payload length, offsetstart, offset length&gt;.
+ *   <li><b>Skipdata</b>:
+ *       <p>Skipdata is interleaved with blocks on 2 levels. Level 0 skip data is interleaved
+ *       between every packed block. Level 1 skip data is interleaved between every 32 packed
+ *       blocks.
+ *   <li><b>Positions, Payloads, and Offsets</b>:
+ *       <p>A position is an integer indicating where the term occurs within one document. A payload
+ *       is a blob of metadata associated with current position. An offset is a pair of integers
+ *       indicating the tokenized start/end offsets for given term in current position: it is
+ *       essentially a specialized payload.
+ *       <p>When payloads and offsets are not omitted, numPositions==numPayloads==numOffsets
+ *       (assuming a null payload contributes one count). As mentioned in block structure, it is
+ *       possible to encode these three either combined or separately.
+ *       <p>In all cases, payloads and offsets are stored together. When encoded as a packed block,
+ *       position data is separated out as .pos, while payloads and offsets are encoded in .pay
+ *       (payload metadata will also be stored directly in .pay). When encoded as VInt blocks, all
+ *       these three are stored interleaved into the .pos (so is payload metadata).
+ *       <p>With this strategy, the majority of payload and offset data will be outside .pos file.
+ *       So for queries that require only position data, running on a full index with payloads and
+ *       offsets, this reduces disk pre-fetches.
+ * </ul>
+ *
+ * <p>Files and detailed format:
+ *
+ * <ul>
+ *   <li><code>.tim</code>: <a href="#Termdictionary">Term Dictionary</a>
+ *   <li><code>.tip</code>: <a href="#Termindex">Term Index</a>
+ *   <li><code>.doc</code>: <a href="#Frequencies">Frequencies and Skip Data</a>
+ *   <li><code>.pos</code>: <a href="#Positions">Positions</a>
+ *   <li><code>.pay</code>: <a href="#Payloads">Payloads and Offsets</a>
+ * </ul>
+ *
+ * <a id="Termdictionary"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Dictionary</b>
+ *       <p>The .tim file contains the list of terms in each field along with per-term statistics
+ *       (such as docfreq) and pointers to the frequencies, positions, payload and skip data in the
+ *       .doc, .pos, and .pay files. See {@link Lucene90BlockTreeTermsWriter} for more details on
+ *       the format.
+ *       <p>NOTE: The term dictionary can plug into different postings implementations: the postings
+ *       writer/reader are actually responsible for encoding and decoding the PostingsHeader and
+ *       TermMetadata sections described here:
+ *       <ul>
+ *         <li>PostingsHeader --&gt; Header, PackedBlockSize
+ *         <li>TermMetadata --&gt; (DocFPDelta|SingletonDocID), PosFPDelta?, PosVIntBlockFPDelta?,
+ *             PayFPDelta?
+ *         <li>Header, --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>PackedBlockSize, SingletonDocID --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>DocFPDelta, PosFPDelta, PayFPDelta, PosVIntBlockFPDelta --&gt; {@link
+ *             DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>Header is a {@link CodecUtil#writeIndexHeader IndexHeader} storing the version
+ *             information for the postings.
+ *         <li>PackedBlockSize is the fixed block size for packed blocks. In packed block, bit width
+ *             is determined by the largest integer. Smaller block size result in smaller variance
+ *             among width of integers hence smaller indexes. Larger block size result in more
+ *             efficient bulk i/o hence better acceleration. This value should always be a multiple
+ *             of 64, currently fixed as 128 as a tradeoff. It is also the skip interval used to
+ *             accelerate {@link org.apache.lucene.index.PostingsEnum#advance(int)}.
+ *         <li>DocFPDelta determines the position of this term's TermFreqs within the .doc file. In
+ *             particular, it is the difference of file offset between this term's data and previous
+ *             term's data (or zero, for the first term in the block).On disk it is stored as the
+ *             difference from previous value in sequence.
+ *         <li>PosFPDelta determines the position of this term's TermPositions within the .pos file.
+ *             While PayFPDelta determines the position of this term's &lt;TermPayloads,
+ *             TermOffsets?&gt; within the .pay file. Similar to DocFPDelta, it is the difference
+ *             between two file positions (or neglected, for fields that omit payloads and offsets).
+ *         <li>PosVIntBlockFPDelta determines the position of this term's last TermPosition in last
+ *             pos packed block within the .pos file. It is synonym for PayVIntBlockFPDelta or
+ *             OffsetVIntBlockFPDelta. This is actually used to indicate whether it is necessary to
+ *             load following payloads and offsets from .pos instead of .pay. Every time a new block
+ *             of positions are to be loaded, the PostingsReader will use this value to check
+ *             whether current block is packed format or VInt. When packed format, payloads and
+ *             offsets are fetched from .pay, otherwise from .pos. (this value is neglected when
+ *             total number of positions i.e. totalTermFreq is less or equal to PackedBlockSize).
+ *         <li>SingletonDocID is an optimization when a term only appears in one document. In this
+ *             case, instead of writing a file pointer to the .doc file (DocFPDelta), and then a
+ *             VIntBlock at that location, the single document ID is written to the term dictionary.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Termindex"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Index</b>
+ *       <p>The .tip file contains an index into the term dictionary, so that it can be accessed
+ *       randomly. See {@link Lucene90BlockTreeTermsWriter} for more details on the format.
+ * </dl>
+ *
+ * <a id="Frequencies"></a>
+ *
+ * <dl>
+ *   <dd><b>Frequencies and Skip Data</b>
+ *       <p>The .doc file contains the lists of documents which contain each term, along with the
+ *       frequency of the term in that document (except when frequencies are omitted: {@link
+ *       IndexOptions#DOCS}). Skip data is saved at the end of each term's postings. The skip data
+ *       is saved once for the entire postings list.
+ *       <ul>
+ *         <li>docFile(.doc) --&gt; Header, &lt;TermFreqs&gt;<sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermFreqs --&gt; &lt;PackedBlock32&gt; <sup>PackedDocBlockNum/32</sup>, VIntBlock?
+ *         <li>PackedBlock32 --&gt; Level1SkipData, &lt;PackedBlock&gt; <sup>32</sup>
+ *         <li>PackedBlock --&gt; Level0SkipData, PackedDocDeltaBlock, PackedFreqBlock?
+ *         <li>VIntBlock --&gt;
+ *             &lt;DocDelta[,Freq?]&gt;<sup>DocFreq-PackedBlockSize*PackedDocBlockNum</sup>
+ *         <li>Level1SkipData --&gt; DocDelta, DocFPDelta, Skip1NumBytes?, ImpactLength?, Impacts?,
+ *             PosFPDelta?, NextPosUpto?, PayFPDelta?, NextPayByteUpto?
+ *         <li>Level0SkipData --&gt; Skip0NumBytes, DocDelta, DocFPDelta, PackedBlockLength,
+ *             ImpactLength?, Impacts?, PosFPDelta?, NextPosUpto?, PayFPDelta?, NextPayByteUpto?
+ *         <li>PackedFreqBlock --&gt; {@link PackedInts PackedInts}, uses patching
+ *         <li>PackedDocDeltaBlock --&gt; {@link PackedInts PackedInts}, does not use patching
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>PackedDocDeltaBlock is theoretically generated from two steps:
+ *             <ol>
+ *               <li>Calculate the difference between each document number and previous one, and get
+ *                   a d-gaps list (for the first document, use absolute value);
+ *               <li>For those d-gaps from first one to
+ *                   PackedDocBlockNum*PackedBlockSize<sup>th</sup>, separately encode as packed
+ *                   blocks.
+ *             </ol>
+ *             If frequencies are not omitted, PackedFreqBlock will be generated without d-gap step.
+ *         <li>VIntBlock stores remaining d-gaps (along with frequencies when possible) with a
+ *             format that encodes DocDelta and Freq:
+ *             <p>DocDelta: if frequencies are indexed, this determines both the document number and
+ *             the frequency. In particular, DocDelta/2 is the difference between this document
+ *             number and the previous document number (or zero when this is the first document in a
+ *             TermFreqs). When DocDelta is odd, the frequency is one. When DocDelta is even, the
+ *             frequency is read as another VInt. If frequencies are omitted, DocDelta contains the
+ *             gap (not multiplied by 2) between document numbers and no frequency information is
+ *             stored.
+ *             <p>For example, the TermFreqs for a term which occurs once in document seven and
+ *             three times in document eleven, with frequencies indexed, would be the following
+ *             sequence of VInts:
+ *             <p>15, 8, 3
+ *             <p>If frequencies were omitted ({@link IndexOptions#DOCS}) it would be this sequence
+ *             of VInts instead:
+ *             <p>7,4
+ *         <li>PackedDocBlockNum is the number of packed blocks for current term's docids or
+ *             frequencies. In particular, PackedDocBlockNum = floor(DocFreq/PackedBlockSize)
+ *         <li>On skip data, DocDelta is the delta between the last doc of the previous block - or
+ *             -1 if there is no previous block - and the last doc of this block. This helps know by
+ *             how much the doc ID should be incremented in case the block gets skipped.
+ *         <li>Skip0Length is the length of skip data at level 0. Encoding it is useful when skip
+ *             data is never needed to quickly skip over skip data, e.g. if only using nextDoc(). It
+ *             is also used when only the first fields of skip data are needed, in order to skip
+ *             over remaining fields without reading them.
+ *         <li>ImpactLength and Impacts are only stored if frequencies are indexed.
+ *         <li>Since positions and payloads are also block encoded, the skip should skip to related
+ *             block first, then fetch the values according to in-block offset. PosFPSkip and
+ *             PayFPSkip record the file offsets of related block in .pos and .pay, respectively.
+ *             While PosBlockOffset indicates which value to fetch inside the related block
+ *             (PayBlockOffset is unnecessary since it is always equal to PosBlockOffset). Same as
+ *             DocFPSkip, the file offsets are relative to the start of current term's TermFreqs,
+ *             and stored as a difference sequence.
+ *         <li>PayByteUpto indicates the start offset of the current payload. It is equivalent to
+ *             the sum of the payload lengths in the current block up to PosBlockOffset
+ *         <li>ImpactLength is the total length of CompetitiveFreqDelta and CompetitiveNormDelta
+ *             pairs. CompetitiveFreqDelta and CompetitiveNormDelta are used to safely skip score
+ *             calculation for uncompetitive documents; See {@link
+ *             org.apache.lucene.codecs.CompetitiveImpactAccumulator} for more details.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Positions"></a>
+ *
+ * <dl>
+ *   <dd><b>Positions</b>
+ *       <p>The .pos file contains the lists of positions that each term occurs at within documents.
+ *       It also sometimes stores part of payloads and offsets for speedup.
+ *       <ul>
+ *         <li>PosFile(.pos) --&gt; Header, &lt;TermPositions&gt; <sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermPositions --&gt; &lt;PackedPosDeltaBlock&gt; <sup>PackedPosBlockNum</sup>,
+ *             VIntBlock?
+ *         <li>VIntBlock --&gt; &lt;PositionDelta[, PayloadLength?], PayloadData?, OffsetDelta?,
+ *             OffsetLength?&gt;<sup>PosVIntCount</sup>
+ *         <li>PackedPosDeltaBlock --&gt; {@link PackedInts PackedInts}
+ *         <li>PositionDelta, OffsetDelta, OffsetLength --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>PayloadData --&gt; {@link DataOutput#writeByte byte}<sup>PayLength</sup>
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>TermPositions are order by term (terms are implicit, from the term dictionary), and
+ *             position values for each term document pair are incremental, and ordered by document
+ *             number.
+ *         <li>PackedPosBlockNum is the number of packed blocks for current term's positions,
+ *             payloads or offsets. In particular, PackedPosBlockNum =
+ *             floor(totalTermFreq/PackedBlockSize)
+ *         <li>PosVIntCount is the number of positions encoded as VInt format. In particular,
+ *             PosVIntCount = totalTermFreq - PackedPosBlockNum*PackedBlockSize
+ *         <li>The procedure how PackedPosDeltaBlock is generated is the same as PackedDocDeltaBlock
+ *             in chapter <a href="#Frequencies">Frequencies and Skip Data</a>.
+ *         <li>PositionDelta is, if payloads are disabled for the term's field, the difference
+ *             between the position of the current occurrence in the document and the previous
+ *             occurrence (or zero, if this is the first occurrence in this document). If payloads
+ *             are enabled for the term's field, then PositionDelta/2 is the difference between the
+ *             current and the previous position. If payloads are enabled and PositionDelta is odd,
+ *             then PayloadLength is stored, indicating the length of the payload at the current
+ *             term position.
+ *         <li>For example, the TermPositions for a term which occurs as the fourth term in one
+ *             document, and as the fifth and ninth term in a subsequent document, would be the
+ *             following sequence of VInts (payloads disabled):
+ *             <p>4, 5, 4
+ *         <li>PayloadData is metadata associated with the current term position. If PayloadLength
+ *             is stored at the current position, then it indicates the length of this payload. If
+ *             PayloadLength is not stored, then this payload has the same length as the payload at
+ *             the previous position.
+ *         <li>OffsetDelta/2 is the difference between this position's startOffset from the previous
+ *             occurrence (or zero, if this is the first occurrence in this document). If
+ *             OffsetDelta is odd, then the length (endOffset-startOffset) differs from the previous
+ *             occurrence and an OffsetLength follows. Offset data is only written for {@link
+ *             IndexOptions#DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS}.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Payloads"></a>
+ *
+ * <dl>
+ *   <dd><b>Payloads and Offsets</b>
+ *       <p>The .pay file will store payloads and offsets associated with certain term-document
+ *       positions. Some payloads and offsets will be separated out into .pos file, for performance
+ *       reasons.
+ *       <ul>
+ *         <li>PayFile(.pay): --&gt; Header, &lt;TermPayloads?, TermOffsets?&gt;
+ *             <sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermPayloads --&gt; &lt;PackedPayLengthBlock, SumPayLength, PayData&gt;
+ *             <sup>PackedPayBlockNum</sup>
+ *         <li>TermOffsets --&gt; &lt;PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock&gt;
+ *             <sup>PackedPayBlockNum</sup>
+ *         <li>PackedPayLengthBlock, PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock --&gt;
+ *             {@link PackedInts PackedInts}
+ *         <li>SumPayLength --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>PayData --&gt; {@link DataOutput#writeByte byte}<sup>SumPayLength</sup>
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>The order of TermPayloads/TermOffsets will be the same as TermPositions, note that
+ *             part of payload/offsets are stored in .pos.
+ *         <li>The procedure how PackedPayLengthBlock and PackedOffsetLengthBlock are generated is
+ *             the same as PackedFreqBlock in chapter <a href="#Frequencies">Frequencies and Skip
+ *             Data</a>. While PackedStartDeltaBlock follows a same procedure as
+ *             PackedDocDeltaBlock.
+ *         <li>PackedPayBlockNum is always equal to PackedPosBlockNum, for the same term. It is also
+ *             synonym for PackedOffsetBlockNum.
+ *         <li>SumPayLength is the total length of payloads written within one block, should be the
+ *             sum of PayLengths in one packed block.
+ *         <li>PayLength in PackedPayLengthBlock is the length of each payload associated with the
+ *             current position.
+ *       </ul>
+ * </dl>
+ *
+ * @lucene.experimental
+ */
+public final class Lucene912PostingsFormat extends PostingsFormat {
+
+  /** Filename extension for some small metadata about how postings are encoded. */
+  public static final String META_EXTENSION = "psm";
+
+  /**
+   * Filename extension for document number, frequencies, and skip data. See chapter: <a
+   * href="#Frequencies">Frequencies and Skip Data</a>
+   */
+  public static final String DOC_EXTENSION = "doc";
+
+  /** Filename extension for positions. See chapter: <a href="#Positions">Positions</a> */
+  public static final String POS_EXTENSION = "pos";
+
+  /**
+   * Filename extension for payloads and offsets. See chapter: <a href="#Payloads">Payloads and
+   * Offsets</a>
+   */
+  public static final String PAY_EXTENSION = "pay";
+
+  /** Size of blocks. */
+  public static final int BLOCK_SIZE = ForUtil.BLOCK_SIZE;
+
+  public static final int BLOCK_MASK = BLOCK_SIZE - 1;
+
+  /** We insert skip data on every block and every SKIP_FACTOR=32 blocks. */
+  public static final int LEVEL1_FACTOR = 32;
+
+  /** Total number of docs covered by level 1 skip data: 32 * 128 = 4,096 */
+  public static final int LEVEL1_NUM_DOCS = LEVEL1_FACTOR * BLOCK_SIZE;
+
+  public static final int LEVEL1_MASK = LEVEL1_NUM_DOCS - 1;
+
+  static final String TERMS_CODEC = "Lucene90PostingsWriterTerms";
+  static final String META_CODEC = "Lucene912PostingsWriterMeta";
+  static final String DOC_CODEC = "Lucene912PostingsWriterDoc";
+  static final String POS_CODEC = "Lucene912PostingsWriterPos";
+  static final String PAY_CODEC = "Lucene912PostingsWriterPay";
+
+  static final int VERSION_START = 0;
+  static final int VERSION_CURRENT = VERSION_START;
+
+  private final int minTermBlockSize;
+  private final int maxTermBlockSize;
+
+  /** Creates {@code Lucene912PostingsFormat} with default settings. */
+  public Lucene912PostingsFormat() {
+    this(
+        Lucene90BlockTreeTermsWriter.DEFAULT_MIN_BLOCK_SIZE,
+        Lucene90BlockTreeTermsWriter.DEFAULT_MAX_BLOCK_SIZE);
+  }
+
+  /**
+   * Creates {@code Lucene912PostingsFormat} with custom values for {@code minBlockSize} and {@code
+   * maxBlockSize} passed to block terms dictionary.
+   *
+   * @see
+   *     Lucene90BlockTreeTermsWriter#Lucene90BlockTreeTermsWriter(SegmentWriteState,PostingsWriterBase,int,int)
+   */
+  public Lucene912PostingsFormat(int minTermBlockSize, int maxTermBlockSize) {
+    super("Lucene912");
+    Lucene90BlockTreeTermsWriter.validateSettings(minTermBlockSize, maxTermBlockSize);
+    this.minTermBlockSize = minTermBlockSize;
+    this.maxTermBlockSize = maxTermBlockSize;
+  }
+
+  @Override
+  public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
+    PostingsWriterBase postingsWriter = new Lucene912PostingsWriter(state);
+    boolean success = false;
+    try {
+      FieldsConsumer ret =
+          new Lucene90BlockTreeTermsWriter(
+              state, postingsWriter, minTermBlockSize, maxTermBlockSize);
+      success = true;
+      return ret;
+    } finally {
+      if (!success) {
+        IOUtils.closeWhileHandlingException(postingsWriter);
+      }
+    }
+  }
+
+  @Override
+  public FieldsProducer fieldsProducer(SegmentReadState state) throws IOException {
+    PostingsReaderBase postingsReader = new Lucene912PostingsReader(state);
+    boolean success = false;
+    try {
+      FieldsProducer ret = new Lucene90BlockTreeTermsReader(postingsReader, state);
+      success = true;
+      return ret;
+    } finally {
+      if (!success) {
+        IOUtils.closeWhileHandlingException(postingsReader);
+      }
+    }
+  }
+
+  /**
+   * Holds all state required for {@link Lucene912PostingsReader} to produce a {@link
+   * org.apache.lucene.index.PostingsEnum} without re-seeking the terms dict.
+   *
+   * @lucene.internal
+   */
+  public static final class IntBlockTermState extends BlockTermState {
+    /** file pointer to the start of the doc ids enumeration, in {@link #DOC_EXTENSION} file */
+    public long docStartFP;
+
+    /** file pointer to the start of the positions enumeration, in {@link #POS_EXTENSION} file */
+    public long posStartFP;
+
+    /** file pointer to the start of the payloads enumeration, in {@link #PAY_EXTENSION} file */
+    public long payStartFP;
+
+    /**
+     * file offset for the last position in the last block, if there are more than {@link
+     * ForUtil#BLOCK_SIZE} positions; otherwise -1
+     *
+     * <p>One might think to use total term frequency to track how many positions are left to read
+     * as we decode the blocks, and decode the last block differently when num_left_positions &lt;
+     * BLOCK_SIZE. Unfortunately this won't work since the tracking will be messed up when we skip
+     * blocks as the skipper will only tell us new position offset (start of block) and number of
+     * positions to skip for that block, without telling us how many positions it has skipped.
+     */
+    public long lastPosBlockOffset;
+
+    /**
+     * docid when there is a single pulsed posting, otherwise -1. freq is always implicitly
+     * totalTermFreq in this case.
+     */
+    public int singletonDocID;
+
+    /** Sole constructor. */
+    public IntBlockTermState() {
+      lastPosBlockOffset = -1;
+      singletonDocID = -1;
+    }
+
+    @Override
+    public IntBlockTermState clone() {
+      IntBlockTermState other = new IntBlockTermState();
+      other.copyFrom(this);
+      return other;
+    }
+
+    @Override
+    public void copyFrom(TermState _other) {
+      super.copyFrom(_other);
+      IntBlockTermState other = (IntBlockTermState) _other;
+      docStartFP = other.docStartFP;
+      posStartFP = other.posStartFP;
+      payStartFP = other.payStartFP;
+      lastPosBlockOffset = other.lastPosBlockOffset;
+      singletonDocID = other.singletonDocID;
+    }
+
+    @Override
+    public String toString() {
+      return super.toString()
+          + " docStartFP="
+          + docStartFP
+          + " posStartFP="
+          + posStartFP
+          + " payStartFP="
+          + payStartFP
+          + " lastPosBlockOffset="
+          + lastPosBlockOffset
+          + " singletonDocID="
+          + singletonDocID;
+    }
+  }
+}

lucene/core/src/java/org/apache/lucene/codecs/lucene912/Lucene912PostingsWriter.java

@@ -0,0 +1,683 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene912;
+
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.BLOCK_SIZE;
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.DOC_CODEC;
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.LEVEL1_MASK;
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.META_CODEC;
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.PAY_CODEC;
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.POS_CODEC;
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.TERMS_CODEC;
+import static org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.VERSION_CURRENT;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.List;
+import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.CompetitiveImpactAccumulator;
+import org.apache.lucene.codecs.PushPostingsWriterBase;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat.IntBlockTermState;
+import org.apache.lucene.index.CorruptIndexException;
+import org.apache.lucene.index.FieldInfo;
+import org.apache.lucene.index.Impact;
+import org.apache.lucene.index.IndexFileNames;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.NumericDocValues;
+import org.apache.lucene.index.SegmentWriteState;
+import org.apache.lucene.store.ByteBuffersDataOutput;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.store.IndexOutput;
+import org.apache.lucene.util.ArrayUtil;
+import org.apache.lucene.util.BitUtil;
+import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.IOUtils;
+
+/** Writer for {@link Lucene912PostingsFormat}. */
+public class Lucene912PostingsWriter extends PushPostingsWriterBase {
+
+  static final IntBlockTermState EMPTY_STATE = new IntBlockTermState();
+
+  IndexOutput metaOut;
+  IndexOutput docOut;
+  IndexOutput posOut;
+  IndexOutput payOut;
+
+  IntBlockTermState lastState;
+
+  // Holds starting file pointers for current term:
+  private long docStartFP;
+  private long posStartFP;
+  private long payStartFP;
+
+  final long[] docDeltaBuffer;
+  final long[] freqBuffer;
+  private int docBufferUpto;
+
+  final long[] posDeltaBuffer;
+  final long[] payloadLengthBuffer;
+  final long[] offsetStartDeltaBuffer;
+  final long[] offsetLengthBuffer;
+  private int posBufferUpto;
+
+  private byte[] payloadBytes;
+  private int payloadByteUpto;
+
+  private int level0LastDocID;
+  private long level0LastPosFP;
+  private long level0LastPayFP;
+
+  private int level1LastDocID;
+  private long level1LastPosFP;
+  private long level1LastPayFP;
+
+  private int docID;
+  private int lastDocID;
+  private int lastPosition;
+  private int lastStartOffset;
+  private int docCount;
+
+  private final PForUtil pforUtil;
+  private final ForDeltaUtil forDeltaUtil;
+
+  private boolean fieldHasNorms;
+  private NumericDocValues norms;
+  private final CompetitiveImpactAccumulator level0FreqNormAccumulator =
+      new CompetitiveImpactAccumulator();
+  private final CompetitiveImpactAccumulator level1CompetitiveFreqNormAccumulator =
+      new CompetitiveImpactAccumulator();
+
+  private int maxNumImpactsAtLevel0;
+  private int maxImpactNumBytesAtLevel0;
+  private int maxNumImpactsAtLevel1;
+  private int maxImpactNumBytesAtLevel1;
+
+  /** Scratch output that we use to be able to prepend the encoded length, e.g. impacts. */
+  private final ByteBuffersDataOutput scratchOutput = ByteBuffersDataOutput.newResettableInstance();
+
+  /**
+   * Output for a single block. This is useful to be able to prepend skip data before each block,
+   * which can only be computed once the block is encoded. The content is then typically copied to
+   * {@link #level1Output}.
+   */
+  private final ByteBuffersDataOutput level0Output = ByteBuffersDataOutput.newResettableInstance();
+
+  /**
+   * Output for groups of 32 blocks. This is useful to prepend skip data for these 32 blocks, which
+   * can only be done once we have encoded these 32 blocks. The content is then typically copied to
+   * {@link #docCount}.
+   */
+  private final ByteBuffersDataOutput level1Output = ByteBuffersDataOutput.newResettableInstance();
+
+  /** Sole constructor. */
+  public Lucene912PostingsWriter(SegmentWriteState state) throws IOException {
+    String metaFileName =
+        IndexFileNames.segmentFileName(
+            state.segmentInfo.name, state.segmentSuffix, Lucene912PostingsFormat.META_EXTENSION);
+    String docFileName =
+        IndexFileNames.segmentFileName(
+            state.segmentInfo.name, state.segmentSuffix, Lucene912PostingsFormat.DOC_EXTENSION);
+    metaOut = state.directory.createOutput(metaFileName, state.context);
+    IndexOutput posOut = null;
+    IndexOutput payOut = null;
+    boolean success = false;
+    try {
+      docOut = state.directory.createOutput(docFileName, state.context);
+      CodecUtil.writeIndexHeader(
+          metaOut, META_CODEC, VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix);
+      CodecUtil.writeIndexHeader(
+          docOut, DOC_CODEC, VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix);
+      final ForUtil forUtil = new ForUtil();
+      forDeltaUtil = new ForDeltaUtil(forUtil);
+      pforUtil = new PForUtil(forUtil);
+      if (state.fieldInfos.hasProx()) {
+        posDeltaBuffer = new long[BLOCK_SIZE];
+        String posFileName =
+            IndexFileNames.segmentFileName(
+                state.segmentInfo.name, state.segmentSuffix, Lucene912PostingsFormat.POS_EXTENSION);
+        posOut = state.directory.createOutput(posFileName, state.context);
+        CodecUtil.writeIndexHeader(
+            posOut, POS_CODEC, VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix);
+
+        if (state.fieldInfos.hasPayloads()) {
+          payloadBytes = new byte[128];
+          payloadLengthBuffer = new long[BLOCK_SIZE];
+        } else {
+          payloadBytes = null;
+          payloadLengthBuffer = null;
+        }
+
+        if (state.fieldInfos.hasOffsets()) {
+          offsetStartDeltaBuffer = new long[BLOCK_SIZE];
+          offsetLengthBuffer = new long[BLOCK_SIZE];
+        } else {
+          offsetStartDeltaBuffer = null;
+          offsetLengthBuffer = null;
+        }
+
+        if (state.fieldInfos.hasPayloads() || state.fieldInfos.hasOffsets()) {
+          String payFileName =
+              IndexFileNames.segmentFileName(
+                  state.segmentInfo.name,
+                  state.segmentSuffix,
+                  Lucene912PostingsFormat.PAY_EXTENSION);
+          payOut = state.directory.createOutput(payFileName, state.context);
+          CodecUtil.writeIndexHeader(
+              payOut, PAY_CODEC, VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix);
+        }
+      } else {
+        posDeltaBuffer = null;
+        payloadLengthBuffer = null;
+        offsetStartDeltaBuffer = null;
+        offsetLengthBuffer = null;
+        payloadBytes = null;
+      }
+      this.payOut = payOut;
+      this.posOut = posOut;
+      success = true;
+    } finally {
+      if (!success) {
+        IOUtils.closeWhileHandlingException(metaOut, docOut, posOut, payOut);
+      }
+    }
+
+    docDeltaBuffer = new long[BLOCK_SIZE];
+    freqBuffer = new long[BLOCK_SIZE];
+  }
+
+  @Override
+  public IntBlockTermState newTermState() {
+    return new IntBlockTermState();
+  }
+
+  @Override
+  public void init(IndexOutput termsOut, SegmentWriteState state) throws IOException {
+    CodecUtil.writeIndexHeader(
+        termsOut, TERMS_CODEC, VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix);
+    termsOut.writeVInt(BLOCK_SIZE);
+  }
+
+  @Override
+  public void setField(FieldInfo fieldInfo) {
+    super.setField(fieldInfo);
+    lastState = EMPTY_STATE;
+    fieldHasNorms = fieldInfo.hasNorms();
+  }
+
+  @Override
+  public void startTerm(NumericDocValues norms) {
+    docStartFP = docOut.getFilePointer();
+    if (writePositions) {
+      posStartFP = posOut.getFilePointer();
+      level1LastPosFP = level0LastPosFP = posStartFP;
+      if (writePayloads || writeOffsets) {
+        payStartFP = payOut.getFilePointer();
+        level1LastPayFP = level0LastPayFP = payStartFP;
+      }
+    }
+    lastDocID = -1;
+    level0LastDocID = -1;
+    level1LastDocID = -1;
+    this.norms = norms;
+    if (writeFreqs) {
+      level0FreqNormAccumulator.clear();
+    }
+  }
+
+  @Override
+  public void startDoc(int docID, int termDocFreq) throws IOException {
+    if (docBufferUpto == BLOCK_SIZE) {
+      flushDocBlock(false);
+      docBufferUpto = 0;
+    }
+
+    final int docDelta = docID - lastDocID;
+
+    if (docID < 0 || docDelta <= 0) {
+      throw new CorruptIndexException(
+          "docs out of order (" + docID + " <= " + lastDocID + " )", docOut);
+    }
+
+    docDeltaBuffer[docBufferUpto] = docDelta;
+    if (writeFreqs) {
+      freqBuffer[docBufferUpto] = termDocFreq;
+    }
+
+    this.docID = docID;
+    lastPosition = 0;
+    lastStartOffset = 0;
+
+    if (writeFreqs) {
+      long norm;
+      if (fieldHasNorms) {
+        boolean found = norms.advanceExact(docID);
+        if (found == false) {
+          // This can happen if indexing hits a problem after adding a doc to the
+          // postings but before buffering the norm. Such documents are written
+          // deleted and will go away on the first merge.
+          norm = 1L;
+        } else {
+          norm = norms.longValue();
+          assert norm != 0 : docID;
+        }
+      } else {
+        norm = 1L;
+      }
+
+      level0FreqNormAccumulator.add(termDocFreq, norm);
+    }
+  }
+
+  @Override
+  public void addPosition(int position, BytesRef payload, int startOffset, int endOffset)
+      throws IOException {
+    if (position > IndexWriter.MAX_POSITION) {
+      throw new CorruptIndexException(
+          "position="
+              + position
+              + " is too large (> IndexWriter.MAX_POSITION="
+              + IndexWriter.MAX_POSITION
+              + ")",
+          docOut);
+    }
+    if (position < 0) {
+      throw new CorruptIndexException("position=" + position + " is < 0", docOut);
+    }
+    posDeltaBuffer[posBufferUpto] = position - lastPosition;
+    if (writePayloads) {
+      if (payload == null || payload.length == 0) {
+        // no payload
+        payloadLengthBuffer[posBufferUpto] = 0;
+      } else {
+        payloadLengthBuffer[posBufferUpto] = payload.length;
+        if (payloadByteUpto + payload.length > payloadBytes.length) {
+          payloadBytes = ArrayUtil.grow(payloadBytes, payloadByteUpto + payload.length);
+        }
+        System.arraycopy(
+            payload.bytes, payload.offset, payloadBytes, payloadByteUpto, payload.length);
+        payloadByteUpto += payload.length;
+      }
+    }
+
+    if (writeOffsets) {
+      assert startOffset >= lastStartOffset;
+      assert endOffset >= startOffset;
+      offsetStartDeltaBuffer[posBufferUpto] = startOffset - lastStartOffset;
+      offsetLengthBuffer[posBufferUpto] = endOffset - startOffset;
+      lastStartOffset = startOffset;
+    }
+
+    posBufferUpto++;
+    lastPosition = position;
+    if (posBufferUpto == BLOCK_SIZE) {
+      pforUtil.encode(posDeltaBuffer, posOut);
+
+      if (writePayloads) {
+        pforUtil.encode(payloadLengthBuffer, payOut);
+        payOut.writeVInt(payloadByteUpto);
+        payOut.writeBytes(payloadBytes, 0, payloadByteUpto);
+        payloadByteUpto = 0;
+      }
+      if (writeOffsets) {
+        pforUtil.encode(offsetStartDeltaBuffer, payOut);
+        pforUtil.encode(offsetLengthBuffer, payOut);
+      }
+      posBufferUpto = 0;
+    }
+  }
+
+  @Override
+  public void finishDoc() throws IOException {
+    docBufferUpto++;
+    docCount++;
+
+    lastDocID = docID;
+  }
+
+  /**
+   * Special vints that are encoded on 2 bytes if they require 15 bits or less. VInt becomes
+   * especially slow when the number of bytes is variable, so this special layout helps in the case
+   * when the number likely requires 15 bits or less
+   */
+  static void writeVInt15(DataOutput out, int v) throws IOException {
+    assert v >= 0;
+    writeVLong15(out, v);
+  }
+
+  /**
+   * @see #writeVInt15(DataOutput, int)
+   */
+  static void writeVLong15(DataOutput out, long v) throws IOException {
+    assert v >= 0;
+    if ((v & ~0x7FFFL) == 0) {
+      out.writeShort((short) v);
+    } else {
+      out.writeShort((short) (0x8000 | (v & 0x7FFF)));
+      out.writeVLong(v >> 15);
+    }
+  }
+
+  private void flushDocBlock(boolean finishTerm) throws IOException {
+    assert docBufferUpto != 0;
+
+    if (docBufferUpto < BLOCK_SIZE) {
+      assert finishTerm;
+      PostingsUtil.writeVIntBlock(
+          level0Output, docDeltaBuffer, freqBuffer, docBufferUpto, writeFreqs);
+    } else {
+      if (writeFreqs) {
+        List<Impact> impacts = level0FreqNormAccumulator.getCompetitiveFreqNormPairs();
+        if (impacts.size() > maxNumImpactsAtLevel0) {
+          maxNumImpactsAtLevel0 = impacts.size();
+        }
+        writeImpacts(impacts, scratchOutput);
+        assert level0Output.size() == 0;
+        if (scratchOutput.size() > maxImpactNumBytesAtLevel0) {
+          maxImpactNumBytesAtLevel0 = Math.toIntExact(scratchOutput.size());
+        }
+        level0Output.writeVLong(scratchOutput.size());
+        scratchOutput.copyTo(level0Output);
+        scratchOutput.reset();
+        if (writePositions) {
+          level0Output.writeVLong(posOut.getFilePointer() - level0LastPosFP);
+          level0Output.writeByte((byte) posBufferUpto);
+          level0LastPosFP = posOut.getFilePointer();
+
+          if (writeOffsets || writePayloads) {
+            level0Output.writeVLong(payOut.getFilePointer() - level0LastPayFP);
+            level0Output.writeVInt(payloadByteUpto);
+            level0LastPayFP = payOut.getFilePointer();
+          }
+        }
+      }
+      long numSkipBytes = level0Output.size();
+      forDeltaUtil.encodeDeltas(docDeltaBuffer, level0Output);
+      if (writeFreqs) {
+        pforUtil.encode(freqBuffer, level0Output);
+      }
+
+      // docID - lastBlockDocID is at least 128, so it can never fit a single byte with a vint
+      // Even if we subtracted 128, only extremely dense blocks would be eligible to a single byte
+      // so let's go with 2 bytes right away
+      writeVInt15(scratchOutput, docID - level0LastDocID);
+      writeVLong15(scratchOutput, level0Output.size());
+      numSkipBytes += scratchOutput.size();
+      level1Output.writeVLong(numSkipBytes);
+      scratchOutput.copyTo(level1Output);
+      scratchOutput.reset();
+    }
+
+    level0Output.copyTo(level1Output);
+    level0Output.reset();
+    level0LastDocID = docID;
+    if (writeFreqs) {
+      level1CompetitiveFreqNormAccumulator.addAll(level0FreqNormAccumulator);
+      level0FreqNormAccumulator.clear();
+    }
+
+    if ((docCount & LEVEL1_MASK) == 0) { // true every 32 blocks (4,096 docs)
+      writeLevel1SkipData();
+      level1LastDocID = docID;
+      level1CompetitiveFreqNormAccumulator.clear();
+    } else if (finishTerm) {
+      level1Output.copyTo(docOut);
+      level1Output.reset();
+      level1CompetitiveFreqNormAccumulator.clear();
+    }
+  }
+
+  private void writeLevel1SkipData() throws IOException {
+    docOut.writeVInt(docID - level1LastDocID);
+    long numImpactBytes = scratchOutput.size();
+    final long level1End;
+    if (writeFreqs) {
+      List<Impact> impacts = level1CompetitiveFreqNormAccumulator.getCompetitiveFreqNormPairs();
+      if (impacts.size() > maxNumImpactsAtLevel1) {
+        maxNumImpactsAtLevel1 = impacts.size();
+      }
+      writeImpacts(impacts, scratchOutput);
+      numImpactBytes = scratchOutput.size();
+      if (numImpactBytes > maxImpactNumBytesAtLevel1) {
+        maxImpactNumBytesAtLevel1 = Math.toIntExact(numImpactBytes);
+      }
+      if (writePositions) {
+        scratchOutput.writeVLong(posOut.getFilePointer() - level1LastPosFP);
+        scratchOutput.writeByte((byte) posBufferUpto);
+        level1LastPosFP = posOut.getFilePointer();
+        if (writeOffsets || writePayloads) {
+          scratchOutput.writeVLong(payOut.getFilePointer() - level1LastPayFP);
+          scratchOutput.writeVInt(payloadByteUpto);
+          level1LastPayFP = payOut.getFilePointer();
+        }
+      }
+      final long level1Len = 2 * Short.BYTES + scratchOutput.size() + level1Output.size();
+      docOut.writeVLong(level1Len);
+      level1End = docOut.getFilePointer() + level1Len;
+      // There are at most 128 impacts, that require at most 2 bytes each
+      assert numImpactBytes <= Short.MAX_VALUE;
+      // Like impacts plus a few vlongs, still way under the max short value
+      assert scratchOutput.size() + Short.BYTES <= Short.MAX_VALUE;
+      docOut.writeShort((short) (scratchOutput.size() + Short.BYTES));
+      docOut.writeShort((short) numImpactBytes);
+      scratchOutput.copyTo(docOut);
+      scratchOutput.reset();
+    } else {
+      docOut.writeVLong(level1Output.size());
+      level1End = docOut.getFilePointer() + level1Output.size();
+    }
+    level1Output.copyTo(docOut);
+    level1Output.reset();
+    assert docOut.getFilePointer() == level1End : docOut.getFilePointer() + " " + level1End;
+  }
+
+  static void writeImpacts(Collection<Impact> impacts, DataOutput out) throws IOException {
+    Impact previous = new Impact(0, 0);
+    for (Impact impact : impacts) {
+      assert impact.freq > previous.freq;
+      assert Long.compareUnsigned(impact.norm, previous.norm) > 0;
+      int freqDelta = impact.freq - previous.freq - 1;
+      long normDelta = impact.norm - previous.norm - 1;
+      if (normDelta == 0) {
+        // most of time, norm only increases by 1, so we can fold everything in a single byte
+        out.writeVInt(freqDelta << 1);
+      } else {
+        out.writeVInt((freqDelta << 1) | 1);
+        out.writeZLong(normDelta);
+      }
+      previous = impact;
+    }
+  }
+
+  /** Called when we are done adding docs to this term */
+  @Override
+  public void finishTerm(BlockTermState _state) throws IOException {
+    IntBlockTermState state = (IntBlockTermState) _state;
+    assert state.docFreq > 0;
+
+    // TODO: wasteful we are counting this (counting # docs
+    // for this term) in two places?
+    assert state.docFreq == docCount : state.docFreq + " vs " + docCount;
+
+    // docFreq == 1, don't write the single docid/freq to a separate file along with a pointer to
+    // it.
+    final int singletonDocID;
+    if (state.docFreq == 1) {
+      // pulse the singleton docid into the term dictionary, freq is implicitly totalTermFreq
+      singletonDocID = (int) docDeltaBuffer[0] - 1;
+    } else {
+      singletonDocID = -1;
+      flushDocBlock(true);
+    }
+
+    final long lastPosBlockOffset;
+
+    if (writePositions) {
+      // totalTermFreq is just total number of positions(or payloads, or offsets)
+      // associated with current term.
+      assert state.totalTermFreq != -1;
+      if (state.totalTermFreq > BLOCK_SIZE) {
+        // record file offset for last pos in last block
+        lastPosBlockOffset = posOut.getFilePointer() - posStartFP;
+      } else {
+        lastPosBlockOffset = -1;
+      }
+      if (posBufferUpto > 0) {
+        assert posBufferUpto < BLOCK_SIZE;
+        // TODO: should we send offsets/payloads to
+        // .pay...?  seems wasteful (have to store extra
+        // vLong for low (< BLOCK_SIZE) DF terms = vast vast
+        // majority)
+
+        // vInt encode the remaining positions/payloads/offsets:
+        int lastPayloadLength = -1; // force first payload length to be written
+        int lastOffsetLength = -1; // force first offset length to be written
+        int payloadBytesReadUpto = 0;
+        for (int i = 0; i < posBufferUpto; i++) {
+          final int posDelta = (int) posDeltaBuffer[i];
+          if (writePayloads) {
+            final int payloadLength = (int) payloadLengthBuffer[i];
+            if (payloadLength != lastPayloadLength) {
+              lastPayloadLength = payloadLength;
+              posOut.writeVInt((posDelta << 1) | 1);
+              posOut.writeVInt(payloadLength);
+            } else {
+              posOut.writeVInt(posDelta << 1);
+            }
+
+            if (payloadLength != 0) {
+              posOut.writeBytes(payloadBytes, payloadBytesReadUpto, payloadLength);
+              payloadBytesReadUpto += payloadLength;
+            }
+          } else {
+            posOut.writeVInt(posDelta);
+          }
+
+          if (writeOffsets) {
+            int delta = (int) offsetStartDeltaBuffer[i];
+            int length = (int) offsetLengthBuffer[i];
+            if (length == lastOffsetLength) {
+              posOut.writeVInt(delta << 1);
+            } else {
+              posOut.writeVInt(delta << 1 | 1);
+              posOut.writeVInt(length);
+              lastOffsetLength = length;
+            }
+          }
+        }
+
+        if (writePayloads) {
+          assert payloadBytesReadUpto == payloadByteUpto;
+          payloadByteUpto = 0;
+        }
+      }
+    } else {
+      lastPosBlockOffset = -1;
+    }
+
+    state.docStartFP = docStartFP;
+    state.posStartFP = posStartFP;
+    state.payStartFP = payStartFP;
+    state.singletonDocID = singletonDocID;
+
+    state.lastPosBlockOffset = lastPosBlockOffset;
+    docBufferUpto = 0;
+    posBufferUpto = 0;
+    lastDocID = -1;
+    docCount = 0;
+  }
+
+  @Override
+  public void encodeTerm(
+      DataOutput out, FieldInfo fieldInfo, BlockTermState _state, boolean absolute)
+      throws IOException {
+    IntBlockTermState state = (IntBlockTermState) _state;
+    if (absolute) {
+      lastState = EMPTY_STATE;
+      assert lastState.docStartFP == 0;
+    }
+
+    if (lastState.singletonDocID != -1
+        && state.singletonDocID != -1
+        && state.docStartFP == lastState.docStartFP) {
+      // With runs of rare values such as ID fields, the increment of pointers in the docs file is
+      // often 0.
+      // Furthermore some ID schemes like auto-increment IDs or Flake IDs are monotonic, so we
+      // encode the delta
+      // between consecutive doc IDs to save space.
+      final long delta = (long) state.singletonDocID - lastState.singletonDocID;
+      out.writeVLong((BitUtil.zigZagEncode(delta) << 1) | 0x01);
+    } else {
+      out.writeVLong((state.docStartFP - lastState.docStartFP) << 1);
+      if (state.singletonDocID != -1) {
+        out.writeVInt(state.singletonDocID);
+      }
+    }
+
+    if (writePositions) {
+      out.writeVLong(state.posStartFP - lastState.posStartFP);
+      if (writePayloads || writeOffsets) {
+        out.writeVLong(state.payStartFP - lastState.payStartFP);
+      }
+    }
+    if (writePositions) {
+      if (state.lastPosBlockOffset != -1) {
+        out.writeVLong(state.lastPosBlockOffset);
+      }
+    }
+    lastState = state;
+  }
+
+  @Override
+  public void close() throws IOException {
+    // TODO: add a finish() at least to PushBase? DV too...?
+    boolean success = false;
+    try {
+      if (docOut != null) {
+        CodecUtil.writeFooter(docOut);
+      }
+      if (posOut != null) {
+        CodecUtil.writeFooter(posOut);
+      }
+      if (payOut != null) {
+        CodecUtil.writeFooter(payOut);
+      }
+      if (metaOut != null) {
+        metaOut.writeInt(maxNumImpactsAtLevel0);
+        metaOut.writeInt(maxImpactNumBytesAtLevel0);
+        metaOut.writeInt(maxNumImpactsAtLevel1);
+        metaOut.writeInt(maxImpactNumBytesAtLevel1);
+        metaOut.writeLong(docOut.getFilePointer());
+        if (posOut != null) {
+          metaOut.writeLong(posOut.getFilePointer());
+          if (payOut != null) {
+            metaOut.writeLong(payOut.getFilePointer());
+          }
+        }
+        CodecUtil.writeFooter(metaOut);
+      }
+      success = true;
+    } finally {
+      if (success) {
+        IOUtils.close(metaOut, docOut, posOut, payOut);
+      } else {
+        IOUtils.closeWhileHandlingException(metaOut, docOut, posOut, payOut);
+      }
+      metaOut = docOut = posOut = payOut = null;
+    }
+  }
+}

lucene/core/src/java/org/apache/lucene/codecs/lucene912/PForUtil.java

@@ -0,0 +1,134 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene912;
+
+import java.io.IOException;
+import java.util.Arrays;
+import org.apache.lucene.store.DataInput;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.LongHeap;
+import org.apache.lucene.util.packed.PackedInts;
+
+/** Utility class to encode sequences of 128 small positive integers. */
+final class PForUtil {
+
+  private static final int MAX_EXCEPTIONS = 7;
+
+  static boolean allEqual(long[] l) {
+    for (int i = 1; i < ForUtil.BLOCK_SIZE; ++i) {
+      if (l[i] != l[0]) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private final ForUtil forUtil;
+
+  PForUtil(ForUtil forUtil) {
+    assert ForUtil.BLOCK_SIZE <= 256 : "blocksize must fit in one byte. got " + ForUtil.BLOCK_SIZE;
+    this.forUtil = forUtil;
+  }
+
+  /** Encode 128 integers from {@code longs} into {@code out}. */
+  void encode(long[] longs, DataOutput out) throws IOException {
+    // Determine the top MAX_EXCEPTIONS + 1 values
+    final LongHeap top = new LongHeap(MAX_EXCEPTIONS + 1);
+    for (int i = 0; i <= MAX_EXCEPTIONS; ++i) {
+      top.push(longs[i]);
+    }
+    long topValue = top.top();
+    for (int i = MAX_EXCEPTIONS + 1; i < ForUtil.BLOCK_SIZE; ++i) {
+      if (longs[i] > topValue) {
+        topValue = top.updateTop(longs[i]);
+      }
+    }
+
+    long max = 0L;
+    for (int i = 1; i <= top.size(); ++i) {
+      max = Math.max(max, top.get(i));
+    }
+
+    final int maxBitsRequired = PackedInts.bitsRequired(max);
+    // We store the patch on a byte, so we can't decrease the number of bits required by more than 8
+    final int patchedBitsRequired =
+        Math.max(PackedInts.bitsRequired(topValue), maxBitsRequired - 8);
+    int numExceptions = 0;
+    final long maxUnpatchedValue = (1L << patchedBitsRequired) - 1;
+    for (int i = 2; i <= top.size(); ++i) {
+      if (top.get(i) > maxUnpatchedValue) {
+        numExceptions++;
+      }
+    }
+    final byte[] exceptions = new byte[numExceptions * 2];
+    if (numExceptions > 0) {
+      int exceptionCount = 0;
+      for (int i = 0; i < ForUtil.BLOCK_SIZE; ++i) {
+        if (longs[i] > maxUnpatchedValue) {
+          exceptions[exceptionCount * 2] = (byte) i;
+          exceptions[exceptionCount * 2 + 1] = (byte) (longs[i] >>> patchedBitsRequired);
+          longs[i] &= maxUnpatchedValue;
+          exceptionCount++;
+        }
+      }
+      assert exceptionCount == numExceptions : exceptionCount + " " + numExceptions;
+    }
+
+    if (allEqual(longs) && maxBitsRequired <= 8) {
+      for (int i = 0; i < numExceptions; ++i) {
+        exceptions[2 * i + 1] =
+            (byte) (Byte.toUnsignedLong(exceptions[2 * i + 1]) << patchedBitsRequired);
+      }
+      out.writeByte((byte) (numExceptions << 5));
+      out.writeVLong(longs[0]);
+    } else {
+      final int token = (numExceptions << 5) | patchedBitsRequired;
+      out.writeByte((byte) token);
+      forUtil.encode(longs, patchedBitsRequired, out);
+    }
+    out.writeBytes(exceptions, exceptions.length);
+  }
+
+  /** Decode 128 integers into {@code ints}. */
+  void decode(PostingIndexInput in, long[] longs) throws IOException {
+    final int token = Byte.toUnsignedInt(in.in.readByte());
+    final int bitsPerValue = token & 0x1f;
+    final int numExceptions = token >>> 5;
+    if (bitsPerValue == 0) {
+      Arrays.fill(longs, 0, ForUtil.BLOCK_SIZE, in.in.readVLong());
+    } else {
+      in.decode(bitsPerValue, longs);
+    }
+    for (int i = 0; i < numExceptions; ++i) {
+      longs[Byte.toUnsignedInt(in.in.readByte())] |=
+          Byte.toUnsignedLong(in.in.readByte()) << bitsPerValue;
+    }
+  }
+
+  /** Skip 128 integers. */
+  void skip(DataInput in) throws IOException {
+    final int token = Byte.toUnsignedInt(in.readByte());
+    final int bitsPerValue = token & 0x1f;
+    final int numExceptions = token >>> 5;
+    if (bitsPerValue == 0) {
+      in.readVLong();
+      in.skipBytes((numExceptions << 1));
+    } else {
+      in.skipBytes(forUtil.numBytes(bitsPerValue) + (numExceptions << 1));
+    }
+  }
+}

lucene/core/src/java/org/apache/lucene/codecs/lucene912/PostingIndexInput.java

@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene912;
+
+import java.io.IOException;
+import org.apache.lucene.internal.vectorization.PostingDecodingUtil;
+import org.apache.lucene.internal.vectorization.VectorizationProvider;
+import org.apache.lucene.store.IndexInput;
+
+/**
+ * Wrapper around an {@link IndexInput} and a {@link ForUtil} that optionally optimizes decoding
+ * using vectorization.
+ */
+public final class PostingIndexInput {
+
+  private static final VectorizationProvider VECTORIZATION_PROVIDER =
+      VectorizationProvider.getInstance();
+
+  public final IndexInput in;
+  public final ForUtil forUtil;
+  private final PostingDecodingUtil postingDecodingUtil;
+
+  public PostingIndexInput(IndexInput in, ForUtil forUtil) throws IOException {
+    this.in = in;
+    this.forUtil = forUtil;
+    this.postingDecodingUtil = VECTORIZATION_PROVIDER.newPostingDecodingUtil(in);
+  }
+
+  /** Decode 128 integers stored on {@code bitsPerValues} bits per value into {@code longs}. */
+  public void decode(int bitsPerValue, long[] longs) throws IOException {
+    forUtil.decode(bitsPerValue, in, postingDecodingUtil, longs);
+  }
+
+  /**
+   * Decode 128 integers stored on {@code bitsPerValues} bits per value, compute their prefix sum,
+   * and store results into {@code longs}.
+   */
+  public void decodeAndPrefixSum(int bitsPerValue, long base, long[] longs) throws IOException {
+    forUtil.decodeAndPrefixSum(bitsPerValue, in, postingDecodingUtil, base, longs);
+  }
+}

lucene/core/src/java/org/apache/lucene/codecs/lucene912/PostingsUtil.java

@@ -0,0 +1,73 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene912;
+
+import java.io.IOException;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.store.IndexInput;
+
+/** Utility class to encode/decode postings block. */
+final class PostingsUtil {
+
+  /**
+   * Read values that have been written using variable-length encoding and group-varint encoding
+   * instead of bit-packing.
+   */
+  static void readVIntBlock(
+      IndexInput docIn,
+      long[] docBuffer,
+      long[] freqBuffer,
+      int num,
+      boolean indexHasFreq,
+      boolean decodeFreq)
+      throws IOException {
+    docIn.readGroupVInts(docBuffer, num);
+    if (indexHasFreq && decodeFreq) {
+      for (int i = 0; i < num; ++i) {
+        freqBuffer[i] = docBuffer[i] & 0x01;
+        docBuffer[i] >>= 1;
+        if (freqBuffer[i] == 0) {
+          freqBuffer[i] = docIn.readVInt();
+        }
+      }
+    } else if (indexHasFreq) {
+      for (int i = 0; i < num; ++i) {
+        docBuffer[i] >>= 1;
+      }
+    }
+  }
+
+  /** Write freq buffer with variable-length encoding and doc buffer with group-varint encoding. */
+  static void writeVIntBlock(
+      DataOutput docOut, long[] docBuffer, long[] freqBuffer, int num, boolean writeFreqs)
+      throws IOException {
+    if (writeFreqs) {
+      for (int i = 0; i < num; i++) {
+        docBuffer[i] = (docBuffer[i] << 1) | (freqBuffer[i] == 1 ? 1 : 0);
+      }
+    }
+    docOut.writeGroupVInts(docBuffer, num);
+    if (writeFreqs) {
+      for (int i = 0; i < num; i++) {
+        final int freq = (int) freqBuffer[i];
+        if (freq != 1) {
+          docOut.writeVInt(freq);
+        }
+      }
+    }
+  }
+}

lucene/core/src/java/org/apache/lucene/codecs/lucene912/gen_ForUtil.py

@@ -0,0 +1,520 @@
+#! /usr/bin/env python
+
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from math import gcd
+
+"""Code generation for ForUtil.java"""
+
+MAX_SPECIALIZED_BITS_PER_VALUE = 24
+OUTPUT_FILE = "ForUtil.java"
+PRIMITIVE_SIZE = [8, 16, 32]
+HEADER = """// This file has been automatically generated, DO NOT EDIT
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene912;
+
+import java.io.IOException;
+import org.apache.lucene.internal.vectorization.PostingDecodingUtil;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.store.IndexInput;
+
+/**
+ * Inspired from https://fulmicoton.com/posts/bitpacking/
+ * Encodes multiple integers in a long to get SIMD-like speedups.
+ * If bitsPerValue <= 8 then we pack 8 ints per long
+ * else if bitsPerValue <= 16 we pack 4 ints per long
+ * else we pack 2 ints per long
+ */
+public final class ForUtil {
+
+  public static final int BLOCK_SIZE = 128;
+  private static final int BLOCK_SIZE_LOG2 = 7;
+
+  private static long expandMask32(long mask32) {
+    return mask32 | (mask32 << 32);
+  }
+
+  private static long expandMask16(long mask16) {
+    return expandMask32(mask16 | (mask16 << 16));
+  }
+
+  private static long expandMask8(long mask8) {
+    return expandMask16(mask8 | (mask8 << 8));
+  }
+
+  private static long mask32(int bitsPerValue) {
+    return expandMask32((1L << bitsPerValue) - 1);
+  }
+
+  private static long mask16(int bitsPerValue) {
+    return expandMask16((1L << bitsPerValue) - 1);
+  }
+
+  private static long mask8(int bitsPerValue) {
+    return expandMask8((1L << bitsPerValue) - 1);
+  }
+
+  private static void expand8(long[] arr) {
+    for (int i = 0; i < 16; ++i) {
+      long l = arr[i];
+      arr[i] = (l >>> 56) & 0xFFL;
+      arr[16 + i] = (l >>> 48) & 0xFFL;
+      arr[32 + i] = (l >>> 40) & 0xFFL;
+      arr[48 + i] = (l >>> 32) & 0xFFL;
+      arr[64 + i] = (l >>> 24) & 0xFFL;
+      arr[80 + i] = (l >>> 16) & 0xFFL;
+      arr[96 + i] = (l >>> 8) & 0xFFL;
+      arr[112 + i] = l & 0xFFL;
+    }
+  }
+
+  private static void expand8To32(long[] arr) {
+    for (int i = 0; i < 16; ++i) {
+      long l = arr[i];
+      arr[i] = (l >>> 24) & 0x000000FF000000FFL;
+      arr[16 + i] = (l >>> 16) & 0x000000FF000000FFL;
+      arr[32 + i] = (l >>> 8) & 0x000000FF000000FFL;
+      arr[48 + i] = l & 0x000000FF000000FFL;
+    }
+  }
+
+  private static void collapse8(long[] arr) {
+    for (int i = 0; i < 16; ++i) {
+      arr[i] =
+          (arr[i] << 56)
+              | (arr[16 + i] << 48)
+              | (arr[32 + i] << 40)
+              | (arr[48 + i] << 32)
+              | (arr[64 + i] << 24)
+              | (arr[80 + i] << 16)
+              | (arr[96 + i] << 8)
+              | arr[112 + i];
+    }
+  }
+
+  private static void expand16(long[] arr) {
+    for (int i = 0; i < 32; ++i) {
+      long l = arr[i];
+      arr[i] = (l >>> 48) & 0xFFFFL;
+      arr[32 + i] = (l >>> 32) & 0xFFFFL;
+      arr[64 + i] = (l >>> 16) & 0xFFFFL;
+      arr[96 + i] = l & 0xFFFFL;
+    }
+  }
+
+  private static void expand16To32(long[] arr) {
+    for (int i = 0; i < 32; ++i) {
+      long l = arr[i];
+      arr[i] = (l >>> 16) & 0x0000FFFF0000FFFFL;
+      arr[32 + i] = l & 0x0000FFFF0000FFFFL;
+    }
+  }
+
+  private static void collapse16(long[] arr) {
+    for (int i = 0; i < 32; ++i) {
+      arr[i] = (arr[i] << 48) | (arr[32 + i] << 32) | (arr[64 + i] << 16) | arr[96 + i];
+    }
+  }
+
+  private static void expand32(long[] arr) {
+    for (int i = 0; i < 64; ++i) {
+      long l = arr[i];
+      arr[i] = l >>> 32;
+      arr[64 + i] = l & 0xFFFFFFFFL;
+    }
+  }
+
+  private static void collapse32(long[] arr) {
+    for (int i = 0; i < 64; ++i) {
+      arr[i] = (arr[i] << 32) | arr[64 + i];
+    }
+  }
+
+  private static void prefixSum8(long[] arr, long base) {
+    expand8To32(arr);
+    prefixSum32(arr, base);
+  }
+
+  private static void prefixSum16(long[] arr, long base) {
+    // We need to move to the next primitive size to avoid overflows
+    expand16To32(arr);
+    prefixSum32(arr, base);
+  }
+
+  private static void prefixSum32(long[] arr, long base) {
+    arr[0] += base << 32;
+    innerPrefixSum32(arr);
+    expand32(arr);
+    final long l = arr[BLOCK_SIZE/2-1];
+    for (int i = BLOCK_SIZE/2; i < BLOCK_SIZE; ++i) {
+      arr[i] += l;
+    }
+  }
+
+  // For some reason unrolling seems to help
+  private static void innerPrefixSum32(long[] arr) {
+    arr[1] += arr[0];
+    arr[2] += arr[1];
+    arr[3] += arr[2];
+    arr[4] += arr[3];
+    arr[5] += arr[4];
+    arr[6] += arr[5];
+    arr[7] += arr[6];
+    arr[8] += arr[7];
+    arr[9] += arr[8];
+    arr[10] += arr[9];
+    arr[11] += arr[10];
+    arr[12] += arr[11];
+    arr[13] += arr[12];
+    arr[14] += arr[13];
+    arr[15] += arr[14];
+    arr[16] += arr[15];
+    arr[17] += arr[16];
+    arr[18] += arr[17];
+    arr[19] += arr[18];
+    arr[20] += arr[19];
+    arr[21] += arr[20];
+    arr[22] += arr[21];
+    arr[23] += arr[22];
+    arr[24] += arr[23];
+    arr[25] += arr[24];
+    arr[26] += arr[25];
+    arr[27] += arr[26];
+    arr[28] += arr[27];
+    arr[29] += arr[28];
+    arr[30] += arr[29];
+    arr[31] += arr[30];
+    arr[32] += arr[31];
+    arr[33] += arr[32];
+    arr[34] += arr[33];
+    arr[35] += arr[34];
+    arr[36] += arr[35];
+    arr[37] += arr[36];
+    arr[38] += arr[37];
+    arr[39] += arr[38];
+    arr[40] += arr[39];
+    arr[41] += arr[40];
+    arr[42] += arr[41];
+    arr[43] += arr[42];
+    arr[44] += arr[43];
+    arr[45] += arr[44];
+    arr[46] += arr[45];
+    arr[47] += arr[46];
+    arr[48] += arr[47];
+    arr[49] += arr[48];
+    arr[50] += arr[49];
+    arr[51] += arr[50];
+    arr[52] += arr[51];
+    arr[53] += arr[52];
+    arr[54] += arr[53];
+    arr[55] += arr[54];
+    arr[56] += arr[55];
+    arr[57] += arr[56];
+    arr[58] += arr[57];
+    arr[59] += arr[58];
+    arr[60] += arr[59];
+    arr[61] += arr[60];
+    arr[62] += arr[61];
+    arr[63] += arr[62];
+  }
+
+  private final long[] tmp = new long[BLOCK_SIZE / 2];
+
+  /** Encode 128 integers from {@code longs} into {@code out}. */
+  void encode(long[] longs, int bitsPerValue, DataOutput out) throws IOException {
+    final int nextPrimitive;
+    final int numLongs;
+    if (bitsPerValue <= 8) {
+      nextPrimitive = 8;
+      numLongs = BLOCK_SIZE / 8;
+      collapse8(longs);
+    } else if (bitsPerValue <= 16) {
+      nextPrimitive = 16;
+      numLongs = BLOCK_SIZE / 4;
+      collapse16(longs);
+    } else {
+      nextPrimitive = 32;
+      numLongs = BLOCK_SIZE / 2;
+      collapse32(longs);
+    }
+
+    final int numLongsPerShift = bitsPerValue * 2;
+    int idx = 0;
+    int shift = nextPrimitive - bitsPerValue;
+    for (int i = 0; i < numLongsPerShift; ++i) {
+      tmp[i] = longs[idx++] << shift;
+    }
+    for (shift = shift - bitsPerValue; shift >= 0; shift -= bitsPerValue) {
+      for (int i = 0; i < numLongsPerShift; ++i) {
+        tmp[i] |= longs[idx++] << shift;
+      }
+    }
+
+    final int remainingBitsPerLong = shift + bitsPerValue;
+    final long maskRemainingBitsPerLong;
+    if (nextPrimitive == 8) {
+      maskRemainingBitsPerLong = MASKS8[remainingBitsPerLong];
+    } else if (nextPrimitive == 16) {
+      maskRemainingBitsPerLong = MASKS16[remainingBitsPerLong];
+    } else {
+      maskRemainingBitsPerLong = MASKS32[remainingBitsPerLong];
+    }
+
+    int tmpIdx = 0;
+    int remainingBitsPerValue = bitsPerValue;
+    while (idx < numLongs) {
+      if (remainingBitsPerValue >= remainingBitsPerLong) {
+        remainingBitsPerValue -= remainingBitsPerLong;
+        tmp[tmpIdx++] |= (longs[idx] >>> remainingBitsPerValue) & maskRemainingBitsPerLong;
+        if (remainingBitsPerValue == 0) {
+          idx++;
+          remainingBitsPerValue = bitsPerValue;
+        }
+      } else {
+        final long mask1, mask2;
+        if (nextPrimitive == 8) {
+          mask1 = MASKS8[remainingBitsPerValue];
+          mask2 = MASKS8[remainingBitsPerLong - remainingBitsPerValue];
+        } else if (nextPrimitive == 16) {
+          mask1 = MASKS16[remainingBitsPerValue];
+          mask2 = MASKS16[remainingBitsPerLong - remainingBitsPerValue];
+        } else {
+          mask1 = MASKS32[remainingBitsPerValue];
+          mask2 = MASKS32[remainingBitsPerLong - remainingBitsPerValue];
+        }
+        tmp[tmpIdx] |= (longs[idx++] & mask1) << (remainingBitsPerLong - remainingBitsPerValue);
+        remainingBitsPerValue = bitsPerValue - remainingBitsPerLong + remainingBitsPerValue;
+        tmp[tmpIdx++] |= (longs[idx] >>> remainingBitsPerValue) & mask2;
+      }
+    }
+
+    for (int i = 0; i < numLongsPerShift; ++i) {
+      out.writeLong(tmp[i]);
+    }
+  }
+
+  /** Number of bytes required to encode 128 integers of {@code bitsPerValue} bits per value. */
+  int numBytes(int bitsPerValue) {
+    return bitsPerValue << (BLOCK_SIZE_LOG2 - 3);
+  }
+
+  private static void decodeSlow(int bitsPerValue, IndexInput in, PostingDecodingUtil pdu, long[] tmp, long[] longs)
+      throws IOException {
+    final int numLongs = bitsPerValue << 1;
+    final long mask = MASKS32[bitsPerValue];
+    pdu.splitLongs(numLongs, longs, 32 - bitsPerValue, mask, tmp, 0, -1L);
+    int longsIdx = numLongs;
+    int shift = 32 - 2 * bitsPerValue;
+    for (; shift >= 0; shift -= bitsPerValue) {
+      shiftLongs(tmp, numLongs, longs, longsIdx, shift, mask);
+      longsIdx += numLongs;
+    }
+    final int remainingBitsPerLong = shift + bitsPerValue;
+    final long mask32RemainingBitsPerLong = MASKS32[remainingBitsPerLong];
+    int tmpIdx = 0;
+    int remainingBits = remainingBitsPerLong;
+    for (; longsIdx < BLOCK_SIZE / 2; ++longsIdx) {
+      int b = bitsPerValue - remainingBits;
+      long l = (tmp[tmpIdx++] & MASKS32[remainingBits]) << b;
+      while (b >= remainingBitsPerLong) {
+        b -= remainingBitsPerLong;
+        l |= (tmp[tmpIdx++] & mask32RemainingBitsPerLong) << b;
+      }
+      if (b > 0) {
+        l |= (tmp[tmpIdx] >>> (remainingBitsPerLong - b)) & MASKS32[b];
+        remainingBits = remainingBitsPerLong - b;
+      } else {
+        remainingBits = remainingBitsPerLong;
+      }
+      longs[longsIdx] = l;
+    }
+  }
+
+  /**
+   * The pattern that this shiftLongs method applies is recognized by the C2 compiler, which
+   * generates SIMD instructions for it in order to shift multiple longs at once.
+   */
+  private static void shiftLongs(long[] a, int count, long[] b, int bi, int shift, long mask) {
+    for (int i = 0; i < count; ++i) {
+      b[bi + i] = (a[i] >>> shift) & mask;
+    }
+  }
+
+  /**
+   * Likewise, but for a simple mask.
+   */
+  private static void maskLongs(long[] a, int count, long[] b, int bi, long mask) {
+    for (int i = 0; i < count; ++i) {
+      b[bi + i] = a[i] & mask;
+    }
+  }
+
+"""
+
+def writeRemainder(bpv, next_primitive, remaining_bits_per_long, o, num_values, f):
+  iteration = 1
+  num_longs = bpv * num_values / remaining_bits_per_long
+  while num_longs % 2 == 0 and num_values % 2 == 0:
+    num_longs /= 2
+    num_values /= 2
+    iteration *= 2
+  f.write('    for (int iter = 0, tmpIdx = 0, longsIdx = %d; iter < %d; ++iter, tmpIdx += %d, longsIdx += %d) {\n' %(o, iteration, num_longs, num_values))
+  i = 0
+  remaining_bits = 0
+  tmp_idx = 0
+  for i in range(int(num_values)):
+    b = bpv
+    if remaining_bits == 0:
+      b -= remaining_bits_per_long
+      f.write('      long l%d = tmp[tmpIdx + %d] << %d;\n' %(i, tmp_idx, b))
+    else:
+      b -= remaining_bits
+      f.write('      long l%d = (tmp[tmpIdx + %d] & MASK%d_%d) << %d;\n' %(i, tmp_idx, next_primitive, remaining_bits, b))
+    tmp_idx += 1
+    while b >= remaining_bits_per_long:
+      b -= remaining_bits_per_long
+      f.write('      l%d |= tmp[tmpIdx + %d] << %d;\n' %(i, tmp_idx, b))
+      tmp_idx += 1
+    if b > 0:
+      f.write('      l%d |= (tmp[tmpIdx + %d] >>> %d) & MASK%d_%d;\n' %(i, tmp_idx, remaining_bits_per_long-b, next_primitive, b))
+      remaining_bits = remaining_bits_per_long-b
+    f.write('      longs[longsIdx + %d] = l%d;\n' %(i, i))
+  f.write('    }\n')
+  
+
+def writeDecode(bpv, f):
+  next_primitive = 32
+  if bpv <= 8:
+    next_primitive = 8
+  elif bpv <= 16:
+    next_primitive = 16
+  f.write('  private static void decode%d(IndexInput in, PostingDecodingUtil pdu, long[] tmp, long[] longs) throws IOException {\n' %bpv)
+  if bpv == next_primitive:
+    f.write('    in.readLongs(longs, 0, %d);\n' %(bpv*2))
+  elif bpv * 2 == next_primitive:
+    f.write('    pdu.splitLongs(%d, longs, %d, MASK%d_%d, longs, %d, MASK%d_%d);\n' %(bpv*2, next_primitive - bpv, next_primitive, bpv, bpv*2, next_primitive, next_primitive - bpv))
+  else:
+    num_values_per_long = 64 / next_primitive
+    f.write('    pdu.splitLongs(%d, longs, %d, MASK%d_%d, tmp, 0, MASK%d_%d);\n' %(bpv*2, next_primitive - bpv, next_primitive, bpv, next_primitive, next_primitive - bpv))
+
+    shift = next_primitive - 2 * bpv
+    o = 2 * bpv
+    while shift >= 0:
+      if shift == 0:
+        f.write('    maskLongs(tmp, %d, longs, %d, MASK%d_%d);\n' %(bpv*2, o, next_primitive, bpv))
+      else:
+        f.write('    shiftLongs(tmp, %d, longs, %d, %d, MASK%d_%d);\n' %(bpv*2, o, shift, next_primitive, bpv))
+      o += bpv*2
+      shift -= bpv
+    remaining_bits = shift + bpv
+    if remaining_bits > 0:
+      if remaining_bits != next_primitive - bpv:
+        # values in tmp still have more bits per value than remaining_bits, clear the higher bits now
+        f.write('    maskLongs(tmp, %d, tmp, 0, MASK%d_%d);\n' %(bpv*2, next_primitive, remaining_bits))
+      writeRemainder(bpv, next_primitive, remaining_bits, o, 128/num_values_per_long - o, f)
+  f.write('  }\n')
+
+
+if __name__ == '__main__':
+  f = open(OUTPUT_FILE, 'w')
+  f.write(HEADER)
+  for primitive_size in PRIMITIVE_SIZE:
+    f.write('  private static final long[] MASKS%d = new long[%d];\n' %(primitive_size, primitive_size))
+  f.write('\n')
+  f.write('  static {\n')
+  for primitive_size in PRIMITIVE_SIZE:
+    f.write('    for (int i = 0; i < %d; ++i) {\n' %primitive_size)
+    f.write('      MASKS%d[i] = mask%d(i);\n' %(primitive_size, primitive_size))
+    f.write('    }\n')
+  f.write('  }')
+  f.write("""
+  // mark values in array as final longs to avoid the cost of reading array, arrays should only be
+  // used when the idx is a variable
+""")
+  for primitive_size in PRIMITIVE_SIZE:
+    for bpv in range(1, min(MAX_SPECIALIZED_BITS_PER_VALUE + 1, primitive_size)):
+      if bpv * 2 != primitive_size or primitive_size == 8:
+        f.write('  private static final long MASK%d_%d = MASKS%d[%d];\n' %(primitive_size, bpv, primitive_size, bpv))
+
+  f.write("""
+  /** Decode 128 integers into {@code longs}. */
+  void decode(int bitsPerValue, IndexInput in, PostingDecodingUtil pdu, long[] longs) throws IOException {
+    switch (bitsPerValue) {
+""")
+  for bpv in range(1, MAX_SPECIALIZED_BITS_PER_VALUE+1):
+    next_primitive = 32
+    if bpv <= 8:
+      next_primitive = 8
+    elif bpv <= 16:
+      next_primitive = 16
+    f.write('      case %d:\n' %bpv)
+    f.write('        decode%d(in, pdu, tmp, longs);\n' %bpv)
+    f.write('        expand%d(longs);\n' %next_primitive)
+    f.write('        break;\n')
+  f.write('      default:\n')
+  f.write('        decodeSlow(bitsPerValue, in, pdu, tmp, longs);\n')
+  f.write('        expand32(longs);\n')
+  f.write('        break;\n')
+  f.write('    }\n')
+  f.write('  }\n')
+
+  f.write("""
+  /**
+   * Delta-decode 128 integers into {@code longs}.
+   */
+  void decodeAndPrefixSum(int bitsPerValue, IndexInput in, PostingDecodingUtil pdu, long base, long[] longs) throws IOException {
+    switch (bitsPerValue) {
+""")
+  for bpv in range(1, MAX_SPECIALIZED_BITS_PER_VALUE+1):
+    next_primitive = 32
+    if bpv <= 8:
+      next_primitive = 8
+    elif bpv <= 16:
+      next_primitive = 16
+    f.write('    case %d:\n' %bpv)
+    f.write('      decode%d(in, pdu, tmp, longs);\n' %bpv)
+    f.write('      prefixSum%d(longs, base);\n' %next_primitive)
+    f.write('      break;\n')
+  f.write('    default:\n')
+  f.write('      decodeSlow(bitsPerValue, in, pdu, tmp, longs);\n')
+  f.write('      prefixSum32(longs, base);\n')
+  f.write('      break;\n')
+  f.write('    }\n')
+  f.write('  }\n')
+
+  f.write('\n')
+  for i in range(1, MAX_SPECIALIZED_BITS_PER_VALUE+1):
+    writeDecode(i, f)
+    if i < MAX_SPECIALIZED_BITS_PER_VALUE:
+      f.write('\n')
+
+  f.write('}\n')

lucene/core/src/java/org/apache/lucene/codecs/lucene912/package-info.java

@@ -0,0 +1,431 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Lucene 9.12 file format.
+ *
+ * <h2>Apache Lucene - Index File Formats</h2>
+ *
+ * <div>
+ *
+ * <ul>
+ *   <li><a href="#Introduction">Introduction</a>
+ *   <li><a href="#Definitions">Definitions</a>
+ *       <ul>
+ *         <li><a href="#Inverted_Indexing">Inverted Indexing</a>
+ *         <li><a href="#Types_of_Fields">Types of Fields</a>
+ *         <li><a href="#Segments">Segments</a>
+ *         <li><a href="#Document_Numbers">Document Numbers</a>
+ *       </ul>
+ *   <li><a href="#Overview">Index Structure Overview</a>
+ *   <li><a href="#File_Naming">File Naming</a>
+ *   <li><a href="#file-names">Summary of File Extensions</a>
+ *       <ul>
+ *         <li><a href="#Lock_File">Lock File</a>
+ *         <li><a href="#History">History</a>
+ *         <li><a href="#Limitations">Limitations</a>
+ *       </ul>
+ * </ul>
+ *
+ * </div> <a id="Introduction"></a>
+ *
+ * <h3>Introduction</h3>
+ *
+ * <div>
+ *
+ * <p>This document defines the index file formats used in this version of Lucene. If you are using
+ * a different version of Lucene, please consult the copy of <code>docs/</code> that was distributed
+ * with the version you are using.
+ *
+ * <p>This document attempts to provide a high-level definition of the Apache Lucene file formats.
+ * </div> <a id="Definitions"></a>
+ *
+ * <h3>Definitions</h3>
+ *
+ * <div>
+ *
+ * <p>The fundamental concepts in Lucene are index, document, field and term.
+ *
+ * <p>An index contains a sequence of documents.
+ *
+ * <ul>
+ *   <li>A document is a sequence of fields.
+ *   <li>A field is a named sequence of terms.
+ *   <li>A term is a sequence of bytes.
+ * </ul>
+ *
+ * <p>The same sequence of bytes in two different fields is considered a different term. Thus terms
+ * are represented as a pair: the string naming the field, and the bytes within the field. <a
+ * id="Inverted_Indexing"></a>
+ *
+ * <h4>Inverted Indexing</h4>
+ *
+ * <p>Lucene's index stores terms and statistics about those terms in order to make term-based
+ * search more efficient. Lucene's terms index falls into the family of indexes known as an
+ * <i>inverted index.</i> This is because it can list, for a term, the documents that contain it.
+ * This is the inverse of the natural relationship, in which documents list terms. <a
+ * id="Types_of_Fields"></a>
+ *
+ * <h4>Types of Fields</h4>
+ *
+ * <p>In Lucene, fields may be <i>stored</i>, in which case their text is stored in the index
+ * literally, in a non-inverted manner. Fields that are inverted are called <i>indexed</i>. A field
+ * may be both stored and indexed.
+ *
+ * <p>The text of a field may be <i>tokenized</i> into terms to be indexed, or the text of a field
+ * may be used literally as a term to be indexed. Most fields are tokenized, but sometimes it is
+ * useful for certain identifier fields to be indexed literally.
+ *
+ * <p>See the {@link org.apache.lucene.document.Field Field} java docs for more information on
+ * Fields. <a id="Segments"></a>
+ *
+ * <h4>Segments</h4>
+ *
+ * <p>Lucene indexes may be composed of multiple sub-indexes, or <i>segments</i>. Each segment is a
+ * fully independent index, which could be searched separately. Indexes evolve by:
+ *
+ * <ol>
+ *   <li>Creating new segments for newly added documents.
+ *   <li>Merging existing segments.
+ * </ol>
+ *
+ * <p>Searches may involve multiple segments and/or multiple indexes, each index potentially
+ * composed of a set of segments. <a id="Document_Numbers"></a>
+ *
+ * <h4>Document Numbers</h4>
+ *
+ * <p>Internally, Lucene refers to documents by an integer <i>document number</i>. The first
+ * document added to an index is numbered zero, and each subsequent document added gets a number one
+ * greater than the previous.
+ *
+ * <p>Note that a document's number may change, so caution should be taken when storing these
+ * numbers outside of Lucene. In particular, numbers may change in the following situations:
+ *
+ * <ul>
+ *   <li>
+ *       <p>The numbers stored in each segment are unique only within the segment, and must be
+ *       converted before they can be used in a larger context. The standard technique is to
+ *       allocate each segment a range of values, based on the range of numbers used in that
+ *       segment. To convert a document number from a segment to an external value, the segment's
+ *       <i>base</i> document number is added. To convert an external value back to a
+ *       segment-specific value, the segment is identified by the range that the external value is
+ *       in, and the segment's base value is subtracted. For example two five document segments
+ *       might be combined, so that the first segment has a base value of zero, and the second of
+ *       five. Document three from the second segment would have an external value of eight.
+ *   <li>
+ *       <p>When documents are deleted, gaps are created in the numbering. These are eventually
+ *       removed as the index evolves through merging. Deleted documents are dropped when segments
+ *       are merged. A freshly-merged segment thus has no gaps in its numbering.
+ * </ul>
+ *
+ * </div> <a id="Overview"></a>
+ *
+ * <h3>Index Structure Overview</h3>
+ *
+ * <div>
+ *
+ * <p>Each segment index maintains the following:
+ *
+ * <ul>
+ *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat Segment info}. This
+ *       contains metadata about a segment, such as the number of documents, what files it uses, and
+ *       information about how the segment is sorted
+ *   <li>{@link org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat Field names}. This
+ *       contains metadata about the set of named fields used in the index.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Stored Field values}.
+ *       This contains, for each document, a list of attribute-value pairs, where the attributes are
+ *       field names. These are used to store auxiliary information about the document, such as its
+ *       title, url, or an identifier to access a database. The set of stored fields are what is
+ *       returned for each hit when searching. This is keyed by document number.
+ *   <li>{@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat Term dictionary}. A
+ *       dictionary containing all of the terms used in all of the indexed fields of all of the
+ *       documents. The dictionary also contains the number of documents which contain the term, and
+ *       pointers to the term's frequency and proximity data.
+ *   <li>{@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat Term Frequency data}. For
+ *       each term in the dictionary, the numbers of all the documents that contain that term, and
+ *       the frequency of the term in that document, unless frequencies are omitted ({@link
+ *       org.apache.lucene.index.IndexOptions#DOCS IndexOptions.DOCS})
+ *   <li>{@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat Term Proximity data}. For
+ *       each term in the dictionary, the positions that the term occurs in each document. Note that
+ *       this will not exist if all fields in all documents omit position data.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90NormsFormat Normalization factors}. For
+ *       each field in each document, a value is stored that is multiplied into the score for hits
+ *       on that field.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vectors}. For each
+ *       field in each document, the term vector (sometimes called document vector) may be stored. A
+ *       term vector consists of term text and term frequency. To add Term Vectors to your index see
+ *       the {@link org.apache.lucene.document.Field Field} constructors
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat Per-document values}. Like
+ *       stored values, these are also keyed by document number, but are generally intended to be
+ *       loaded into main memory for fast access. Whereas stored values are generally intended for
+ *       summary results from searches, per-document values are useful for things like scoring
+ *       factors.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat Live documents}. An
+ *       optional file indicating which documents are live.
+ *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90PointsFormat Point values}. Optional pair
+ *       of files, recording dimensionally indexed fields, to enable fast numeric range filtering
+ *       and large numeric values like BigInteger and BigDecimal (1D) and geographic shape
+ *       intersection (2D, 3D).
+ *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat Vector values}. The
+ *       vector format stores numeric vectors in a format optimized for random access and
+ *       computation, supporting high-dimensional nearest-neighbor search.
+ * </ul>
+ *
+ * <p>Details on each of these are provided in their linked pages. </div> <a id="File_Naming"></a>
+ *
+ * <h3>File Naming</h3>
+ *
+ * <div>
+ *
+ * <p>All files belonging to a segment have the same name with varying extensions. The extensions
+ * correspond to the different file formats described below. When using the Compound File format
+ * (default for small segments) these files (except for the Segment info file, the Lock file, and
+ * Deleted documents file) are collapsed into a single .cfs file (see below for details)
+ *
+ * <p>Typically, all segments in an index are stored in a single directory, although this is not
+ * required.
+ *
+ * <p>File names are never re-used. That is, when any file is saved to the Directory it is given a
+ * never before used filename. This is achieved using a simple generations approach. For example,
+ * the first segments file is segments_1, then segments_2, etc. The generation is a sequential long
+ * integer represented in alpha-numeric (base 36) form. </div> <a id="file-names"></a>
+ *
+ * <h3>Summary of File Extensions</h3>
+ *
+ * <div>
+ *
+ * <p>The following table summarizes the names and extensions of the files in Lucene:
+ *
+ * <table class="padding4" style="border-spacing: 1px; border-collapse: separate">
+ * <caption>lucene filenames by extension</caption>
+ * <tr>
+ * <th>Name</th>
+ * <th>Extension</th>
+ * <th>Brief Description</th>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.index.SegmentInfos Segments File}</td>
+ * <td>segments_N</td>
+ * <td>Stores information about a commit point</td>
+ * </tr>
+ * <tr>
+ * <td><a href="#Lock_File">Lock File</a></td>
+ * <td>write.lock</td>
+ * <td>The Write lock prevents multiple IndexWriters from writing to the same
+ * file.</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat Segment Info}</td>
+ * <td>.si</td>
+ * <td>Stores metadata about a segment</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90CompoundFormat Compound File}</td>
+ * <td>.cfs, .cfe</td>
+ * <td>An optional "virtual" file consisting of all the other index files for
+ * systems that frequently run out of file handles.</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat Fields}</td>
+ * <td>.fnm</td>
+ * <td>Stores information about the fields</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Field Index}</td>
+ * <td>.fdx</td>
+ * <td>Contains pointers to field data</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Field Data}</td>
+ * <td>.fdt</td>
+ * <td>The stored fields for documents</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat Term Dictionary}</td>
+ * <td>.tim</td>
+ * <td>The term dictionary, stores term info</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat Term Index}</td>
+ * <td>.tip</td>
+ * <td>The index into the Term Dictionary</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat Frequencies}</td>
+ * <td>.doc</td>
+ * <td>Contains the list of docs which contain each term along with frequency</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat Positions}</td>
+ * <td>.pos</td>
+ * <td>Stores position information about where a term occurs in the index</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat Payloads}</td>
+ * <td>.pay</td>
+ * <td>Stores additional per-position metadata information such as character offsets and user payloads</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90NormsFormat Norms}</td>
+ * <td>.nvd, .nvm</td>
+ * <td>Encodes length and boost factors for docs and fields</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat Per-Document Values}</td>
+ * <td>.dvd, .dvm</td>
+ * <td>Encodes additional scoring factors or other per-document information.</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vector Index}</td>
+ * <td>.tvx</td>
+ * <td>Stores offset into the document data file</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vector Data}</td>
+ * <td>.tvd</td>
+ * <td>Contains term vector data.</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat Live Documents}</td>
+ * <td>.liv</td>
+ * <td>Info about what documents are live</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90PointsFormat Point values}</td>
+ * <td>.dii, .dim</td>
+ * <td>Holds indexed points</td>
+ * </tr>
+ * <tr>
+ * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat Vector values}</td>
+ * <td>.vec, .vem, .veq, vex</td>
+ * <td>Holds indexed vectors; <code>.vec</code> files contain the raw vector data,
+ * <code>.vem</code> the vector metadata, <code>.veq</code> the quantized vector data, and <code>.vex</code> the
+ * hnsw graph data.</td>
+ * </tr>
+ * </table>
+ *
+ * </div> <a id="Lock_File"></a>
+ *
+ * <h3>Lock File</h3>
+ *
+ * The write lock, which is stored in the index directory by default, is named "write.lock". If the
+ * lock directory is different from the index directory then the write lock will be named
+ * "XXXX-write.lock" where XXXX is a unique prefix derived from the full path to the index
+ * directory. When this file is present, a writer is currently modifying the index (adding or
+ * removing documents). This lock file ensures that only one writer is modifying the index at a
+ * time. <a id="History"></a>
+ *
+ * <h3>History</h3>
+ *
+ * <p>Compatibility notes are provided in this document, describing how file formats have changed
+ * from prior versions:
+ *
+ * <ul>
+ *   <li>In version 2.1, the file format was changed to allow lock-less commits (ie, no more commit
+ *       lock). The change is fully backwards compatible: you can open a pre-2.1 index for searching
+ *       or adding/deleting of docs. When the new segments file is saved (committed), it will be
+ *       written in the new file format (meaning no specific "upgrade" process is needed). But note
+ *       that once a commit has occurred, pre-2.1 Lucene will not be able to read the index.
+ *   <li>In version 2.3, the file format was changed to allow segments to share a single set of doc
+ *       store (vectors &amp; stored fields) files. This allows for faster indexing in certain
+ *       cases. The change is fully backwards compatible (in the same way as the lock-less commits
+ *       change in 2.1).
+ *   <li>In version 2.4, Strings are now written as true UTF-8 byte sequence, not Java's modified
+ *       UTF-8. See <a href="http://issues.apache.org/jira/browse/LUCENE-510">LUCENE-510</a> for
+ *       details.
+ *   <li>In version 2.9, an optional opaque Map&lt;String,String&gt; CommitUserData may be passed to
+ *       IndexWriter's commit methods (and later retrieved), which is recorded in the segments_N
+ *       file. See <a href="http://issues.apache.org/jira/browse/LUCENE-1382">LUCENE-1382</a> for
+ *       details. Also, diagnostics were added to each segment written recording details about why
+ *       it was written (due to flush, merge; which OS/JRE was used; etc.). See issue <a
+ *       href="http://issues.apache.org/jira/browse/LUCENE-1654">LUCENE-1654</a> for details.
+ *   <li>In version 3.0, compressed fields are no longer written to the index (they can still be
+ *       read, but on merge the new segment will write them, uncompressed). See issue <a
+ *       href="http://issues.apache.org/jira/browse/LUCENE-1960">LUCENE-1960</a> for details.
+ *   <li>In version 3.1, segments records the code version that created them. See <a
+ *       href="http://issues.apache.org/jira/browse/LUCENE-2720">LUCENE-2720</a> for details.
+ *       Additionally segments track explicitly whether or not they have term vectors. See <a
+ *       href="http://issues.apache.org/jira/browse/LUCENE-2811">LUCENE-2811</a> for details.
+ *   <li>In version 3.2, numeric fields are written as natively to stored fields file, previously
+ *       they were stored in text format only.
+ *   <li>In version 3.4, fields can omit position data while still indexing term frequencies.
+ *   <li>In version 4.0, the format of the inverted index became extensible via the {@link
+ *       org.apache.lucene.codecs.Codec Codec} api. Fast per-document storage ({@code DocValues})
+ *       was introduced. Normalization factors need no longer be a single byte, they can be any
+ *       {@link org.apache.lucene.index.NumericDocValues NumericDocValues}. Terms need not be
+ *       unicode strings, they can be any byte sequence. Term offsets can optionally be indexed into
+ *       the postings lists. Payloads can be stored in the term vectors.
+ *   <li>In version 4.1, the format of the postings list changed to use either of FOR compression or
+ *       variable-byte encoding, depending upon the frequency of the term. Terms appearing only once
+ *       were changed to inline directly into the term dictionary. Stored fields are compressed by
+ *       default.
+ *   <li>In version 4.2, term vectors are compressed by default. DocValues has a new multi-valued
+ *       type (SortedSet), that can be used for faceting/grouping/joining on multi-valued fields.
+ *   <li>In version 4.5, DocValues were extended to explicitly represent missing values.
+ *   <li>In version 4.6, FieldInfos were extended to support per-field DocValues generation, to
+ *       allow updating NumericDocValues fields.
+ *   <li>In version 4.8, checksum footers were added to the end of each index file for improved data
+ *       integrity. Specifically, the last 8 bytes of every index file contain the zlib-crc32
+ *       checksum of the file.
+ *   <li>In version 4.9, DocValues has a new multi-valued numeric type (SortedNumeric) that is
+ *       suitable for faceting/sorting/analytics.
+ *   <li>In version 5.4, DocValues have been improved to store more information on disk: addresses
+ *       for binary fields and ord indexes for multi-valued fields.
+ *   <li>In version 6.0, Points were added, for multi-dimensional range/distance search.
+ *   <li>In version 6.2, new Segment info format that reads/writes the index sort, to support index
+ *       sorting.
+ *   <li>In version 7.0, DocValues have been improved to better support sparse doc values thanks to
+ *       an iterator API.
+ *   <li>In version 8.0, postings have been enhanced to record, for each block of doc ids, the (term
+ *       freq, normalization factor) pairs that may trigger the maximum score of the block. This
+ *       information is recorded alongside skip data in order to be able to skip blocks of doc ids
+ *       if they may not produce high enough scores. Additionally doc values and norms has been
+ *       extended with jump-tables to make access O(1) instead of O(n), where n is the number of
+ *       elements to skip when advancing in the data.
+ *   <li>In version 8.4, postings, positions, offsets and payload lengths have move to a more
+ *       performant encoding that is vectorized.
+ *   <li>In version 8.6, index sort serialization is delegated to the sorts themselves, to allow
+ *       user-defined sorts to be used
+ *   <li>In version 8.7, stored fields compression became adaptive to better handle documents with
+ *       smaller stored fields.
+ *   <li>In version 9.0, vector-valued fields were added.
+ *   <li>In version 9.1, vector-valued fields were modified to add a graph hierarchy.
+ *   <li>In version 9.2, docs of vector-valued fields were moved from .vem to .vec and encoded by
+ *       IndexDISI. ordToDoc mappings was added to .vem.
+ *   <li>In version 9.5, HNSW graph connections were changed to be delta-encoded with vints.
+ *       Additionally, metadata file size improvements were made by delta-encoding nodes by graph
+ *       layer and not writing the node ids for the zeroth layer.
+ *   <li>In version 9.9, Vector scalar quantization support was added. Allowing the HNSW vector
+ *       format to utilize int8 quantized vectors for float32 vector search.
+ *   <li>In version 9.12, skip data was refactored to have only two levels: every 128 docs and every
+ *       4,06 docs, and to be inlined in postings lists. This resulted in a speedup for queries that
+ *       need skipping, especially conjunctions.
+ * </ul>
+ *
+ * <a id="Limitations"></a>
+ *
+ * <h3>Limitations</h3>
+ *
+ * <div>
+ *
+ * <p>Lucene uses a Java <code>int</code> to refer to document numbers, and the index file format
+ * uses an <code>Int32</code> on-disk to store document numbers. This is a limitation of both the
+ * index file format and the current implementation. Eventually these should be replaced with either
+ * <code>UInt64</code> values, or better yet, {@link org.apache.lucene.store.DataOutput#writeVInt
+ * VInt} values which have no limit. </div>
+ */
+package org.apache.lucene.codecs.lucene912;

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsReader.java

@@ -68,10 +68,10 @@ public final class Lucene99HnswVectorsReader extends KnnVectorsReader
   private static final long SHALLOW_SIZE =
       RamUsageEstimator.shallowSizeOfInstance(Lucene99HnswVectorsFormat.class);
 
+  private final FlatVectorsReader flatVectorsReader;
   private final FieldInfos fieldInfos;
   private final Map<String, FieldEntry> fields = new HashMap<>();
   private final IndexInput vectorIndex;
-  private final FlatVectorsReader flatVectorsReader;
 
   public Lucene99HnswVectorsReader(SegmentReadState state, FlatVectorsReader flatVectorsReader)
       throws IOException {
@@ -93,13 +93,13 @@ public final class Lucene99HnswVectorsReader extends KnnVectorsReader
                 Lucene99HnswVectorsFormat.VERSION_CURRENT,
                 state.segmentInfo.getId(),
                 state.segmentSuffix);
-        readFields(meta, state.fieldInfos);
+        readFields(meta);
       } catch (Throwable exception) {
         priorE = exception;
       } finally {
         CodecUtil.checkFooter(meta, priorE);
       }
-      vectorIndex =
+      this.vectorIndex =
           openDataInput(
               state,
               versionMeta,
@@ -154,9 +154,9 @@ public final class Lucene99HnswVectorsReader extends KnnVectorsReader
     }
   }
 
-  private void readFields(ChecksumIndexInput meta, FieldInfos infos) throws IOException {
+  private void readFields(ChecksumIndexInput meta) throws IOException {
     for (int fieldNumber = meta.readInt(); fieldNumber != -1; fieldNumber = meta.readInt()) {
-      FieldInfo info = infos.fieldInfo(fieldNumber);
+      FieldInfo info = fieldInfos.fieldInfo(fieldNumber);
       if (info == null) {
         throw new CorruptIndexException("Invalid field number: " + fieldNumber, meta);
       }
@@ -463,6 +463,7 @@ public final class Lucene99HnswVectorsReader extends KnnVectorsReader
       // unsafe; no bounds checking
       dataIn.seek(graphLevelNodeOffsets.get(targetIndex + graphLevelNodeIndexOffsets[level]));
       arcCount = dataIn.readVInt();
+      assert arcCount <= currentNeighborsBuffer.length : "too many neighbors: " + arcCount;
       if (arcCount > 0) {
         currentNeighborsBuffer[0] = dataIn.readVInt();
         for (int i = 1; i < arcCount; i++) {

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsWriter.java

@@ -612,10 +612,10 @@ public final class Lucene99HnswVectorsWriter extends KnnVectorsWriter {
       throw new UnsupportedOperationException();
     }
 
-    OnHeapHnswGraph getGraph() {
+    OnHeapHnswGraph getGraph() throws IOException {
       assert flatFieldVectorsWriter.isFinished();
       if (node > 0) {
-        return hnswGraphBuilder.getGraph();
+        return hnswGraphBuilder.getCompletedGraph();
       } else {
         return null;
       }

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99ScalarQuantizedVectorsWriter.java

@@ -677,6 +677,10 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
       Float confidenceInterval,
       byte bits)
       throws IOException {
+    if (vectorSimilarityFunction == VectorSimilarityFunction.COSINE) {
+      floatVectorValues = new NormalizedFloatVectorValues(floatVectorValues);
+      vectorSimilarityFunction = VectorSimilarityFunction.DOT_PRODUCT;
+    }
     if (confidenceInterval != null && confidenceInterval == DYNAMIC_CONFIDENCE_INTERVAL) {
       return ScalarQuantizer.fromVectorsAutoInterval(
           floatVectorValues, vectorSimilarityFunction, numVectors, bits);
@@ -797,10 +801,9 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
       if (floatVectors.size() == 0) {
         return new ScalarQuantizer(0, 0, bits);
       }
-      FloatVectorValues floatVectorValues = new FloatVectorWrapper(floatVectors, normalize);
       ScalarQuantizer quantizer =
           buildScalarQuantizer(
-              floatVectorValues,
+              new FloatVectorWrapper(floatVectors),
               floatVectors.size(),
               fieldInfo.getVectorSimilarityFunction(),
               confidenceInterval,
@@ -851,14 +854,10 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
 
   static class FloatVectorWrapper extends FloatVectorValues {
     private final List<float[]> vectorList;
-    private final float[] copy;
-    private final boolean normalize;
     protected int curDoc = -1;
 
-    FloatVectorWrapper(List<float[]> vectorList, boolean normalize) {
+    FloatVectorWrapper(List<float[]> vectorList) {
       this.vectorList = vectorList;
-      this.copy = new float[vectorList.get(0).length];
-      this.normalize = normalize;
     }
 
     @Override
@@ -876,11 +875,6 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
       if (curDoc == -1 || curDoc >= vectorList.size()) {
         throw new IOException("Current doc not set or too many iterations");
       }
-      if (normalize) {
-        System.arraycopy(vectorList.get(curDoc), 0, copy, 0, copy.length);
-        VectorUtil.l2normalize(copy);
-        return copy;
-      }
       return vectorList.get(curDoc);
     }
 
@@ -949,13 +943,16 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
               // quantization?
               || scalarQuantizer.getBits() <= 4
               || shouldRequantize(reader.getQuantizationState(fieldInfo.name), scalarQuantizer)) {
+            FloatVectorValues toQuantize =
+                mergeState.knnVectorsReaders[i].getFloatVectorValues(fieldInfo.name);
+            if (fieldInfo.getVectorSimilarityFunction() == VectorSimilarityFunction.COSINE) {
+              toQuantize = new NormalizedFloatVectorValues(toQuantize);
+            }
             sub =
                 new QuantizedByteVectorValueSub(
                     mergeState.docMaps[i],
                     new QuantizedFloatVectorValues(
-                        mergeState.knnVectorsReaders[i].getFloatVectorValues(fieldInfo.name),
-                        fieldInfo.getVectorSimilarityFunction(),
-                        scalarQuantizer));
+                        toQuantize, fieldInfo.getVectorSimilarityFunction(), scalarQuantizer));
           } else {
             sub =
                 new QuantizedByteVectorValueSub(
@@ -1042,7 +1039,6 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
     private final FloatVectorValues values;
     private final ScalarQuantizer quantizer;
     private final byte[] quantizedVector;
-    private final float[] normalizedVector;
     private float offsetValue = 0f;
 
     private final VectorSimilarityFunction vectorSimilarityFunction;
@@ -1055,11 +1051,6 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
       this.quantizer = quantizer;
       this.quantizedVector = new byte[values.dimension()];
       this.vectorSimilarityFunction = vectorSimilarityFunction;
-      if (vectorSimilarityFunction == VectorSimilarityFunction.COSINE) {
-        this.normalizedVector = new float[values.dimension()];
-      } else {
-        this.normalizedVector = null;
-      }
     }
 
     @Override
@@ -1111,15 +1102,8 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
     }
 
     private void quantize() throws IOException {
-      if (vectorSimilarityFunction == VectorSimilarityFunction.COSINE) {
-        System.arraycopy(values.vectorValue(), 0, normalizedVector, 0, normalizedVector.length);
-        VectorUtil.l2normalize(normalizedVector);
-        offsetValue =
-            quantizer.quantize(normalizedVector, quantizedVector, vectorSimilarityFunction);
-      } else {
-        offsetValue =
-            quantizer.quantize(values.vectorValue(), quantizedVector, vectorSimilarityFunction);
-      }
+      offsetValue =
+          quantizer.quantize(values.vectorValue(), quantizedVector, vectorSimilarityFunction);
     }
   }
 
@@ -1216,4 +1200,60 @@ public final class Lucene99ScalarQuantizedVectorsWriter extends FlatVectorsWrite
       throw new UnsupportedOperationException();
     }
   }
+
+  static final class NormalizedFloatVectorValues extends FloatVectorValues {
+    private final FloatVectorValues values;
+    private final float[] normalizedVector;
+    int curDoc = -1;
+
+    public NormalizedFloatVectorValues(FloatVectorValues values) {
+      this.values = values;
+      this.normalizedVector = new float[values.dimension()];
+    }
+
+    @Override
+    public int dimension() {
+      return values.dimension();
+    }
+
+    @Override
+    public int size() {
+      return values.size();
+    }
+
+    @Override
+    public float[] vectorValue() throws IOException {
+      return normalizedVector;
+    }
+
+    @Override
+    public VectorScorer scorer(float[] query) throws IOException {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public int docID() {
+      return values.docID();
+    }
+
+    @Override
+    public int nextDoc() throws IOException {
+      curDoc = values.nextDoc();
+      if (curDoc != NO_MORE_DOCS) {
+        System.arraycopy(values.vectorValue(), 0, normalizedVector, 0, normalizedVector.length);
+        VectorUtil.l2normalize(normalizedVector);
+      }
+      return curDoc;
+    }
+
+    @Override
+    public int advance(int target) throws IOException {
+      curDoc = values.advance(target);
+      if (curDoc != NO_MORE_DOCS) {
+        System.arraycopy(values.vectorValue(), 0, normalizedVector, 0, normalizedVector.length);
+        VectorUtil.l2normalize(normalizedVector);
+      }
+      return curDoc;
+    }
+  }
 }

lucene/core/src/java/org/apache/lucene/codecs/lucene99/package-info.java

@@ -15,414 +15,5 @@
  * limitations under the License.
  */
 
-/**
- * Lucene 9.9 file format.
- *
- * <h2>Apache Lucene - Index File Formats</h2>
- *
- * <div>
- *
- * <ul>
- *   <li><a href="#Introduction">Introduction</a>
- *   <li><a href="#Definitions">Definitions</a>
- *       <ul>
- *         <li><a href="#Inverted_Indexing">Inverted Indexing</a>
- *         <li><a href="#Types_of_Fields">Types of Fields</a>
- *         <li><a href="#Segments">Segments</a>
- *         <li><a href="#Document_Numbers">Document Numbers</a>
- *       </ul>
- *   <li><a href="#Overview">Index Structure Overview</a>
- *   <li><a href="#File_Naming">File Naming</a>
- *   <li><a href="#file-names">Summary of File Extensions</a>
- *       <ul>
- *         <li><a href="#Lock_File">Lock File</a>
- *         <li><a href="#History">History</a>
- *         <li><a href="#Limitations">Limitations</a>
- *       </ul>
- * </ul>
- *
- * </div> <a id="Introduction"></a>
- *
- * <h3>Introduction</h3>
- *
- * <div>
- *
- * <p>This document defines the index file formats used in this version of Lucene. If you are using
- * a different version of Lucene, please consult the copy of <code>docs/</code> that was distributed
- * with the version you are using.
- *
- * <p>This document attempts to provide a high-level definition of the Apache Lucene file formats.
- * </div> <a id="Definitions"></a>
- *
- * <h3>Definitions</h3>
- *
- * <div>
- *
- * <p>The fundamental concepts in Lucene are index, document, field and term.
- *
- * <p>An index contains a sequence of documents.
- *
- * <ul>
- *   <li>A document is a sequence of fields.
- *   <li>A field is a named sequence of terms.
- *   <li>A term is a sequence of bytes.
- * </ul>
- *
- * <p>The same sequence of bytes in two different fields is considered a different term. Thus terms
- * are represented as a pair: the string naming the field, and the bytes within the field. <a
- * id="Inverted_Indexing"></a>
- *
- * <h4>Inverted Indexing</h4>
- *
- * <p>Lucene's index stores terms and statistics about those terms in order to make term-based
- * search more efficient. Lucene's terms index falls into the family of indexes known as an
- * <i>inverted index.</i> This is because it can list, for a term, the documents that contain it.
- * This is the inverse of the natural relationship, in which documents list terms. <a
- * id="Types_of_Fields"></a>
- *
- * <h4>Types of Fields</h4>
- *
- * <p>In Lucene, fields may be <i>stored</i>, in which case their text is stored in the index
- * literally, in a non-inverted manner. Fields that are inverted are called <i>indexed</i>. A field
- * may be both stored and indexed.
- *
- * <p>The text of a field may be <i>tokenized</i> into terms to be indexed, or the text of a field
- * may be used literally as a term to be indexed. Most fields are tokenized, but sometimes it is
- * useful for certain identifier fields to be indexed literally.
- *
- * <p>See the {@link org.apache.lucene.document.Field Field} java docs for more information on
- * Fields. <a id="Segments"></a>
- *
- * <h4>Segments</h4>
- *
- * <p>Lucene indexes may be composed of multiple sub-indexes, or <i>segments</i>. Each segment is a
- * fully independent index, which could be searched separately. Indexes evolve by:
- *
- * <ol>
- *   <li>Creating new segments for newly added documents.
- *   <li>Merging existing segments.
- * </ol>
- *
- * <p>Searches may involve multiple segments and/or multiple indexes, each index potentially
- * composed of a set of segments. <a id="Document_Numbers"></a>
- *
- * <h4>Document Numbers</h4>
- *
- * <p>Internally, Lucene refers to documents by an integer <i>document number</i>. The first
- * document added to an index is numbered zero, and each subsequent document added gets a number one
- * greater than the previous.
- *
- * <p>Note that a document's number may change, so caution should be taken when storing these
- * numbers outside of Lucene. In particular, numbers may change in the following situations:
- *
- * <ul>
- *   <li>
- *       <p>The numbers stored in each segment are unique only within the segment, and must be
- *       converted before they can be used in a larger context. The standard technique is to
- *       allocate each segment a range of values, based on the range of numbers used in that
- *       segment. To convert a document number from a segment to an external value, the segment's
- *       <i>base</i> document number is added. To convert an external value back to a
- *       segment-specific value, the segment is identified by the range that the external value is
- *       in, and the segment's base value is subtracted. For example two five document segments
- *       might be combined, so that the first segment has a base value of zero, and the second of
- *       five. Document three from the second segment would have an external value of eight.
- *   <li>
- *       <p>When documents are deleted, gaps are created in the numbering. These are eventually
- *       removed as the index evolves through merging. Deleted documents are dropped when segments
- *       are merged. A freshly-merged segment thus has no gaps in its numbering.
- * </ul>
- *
- * </div> <a id="Overview"></a>
- *
- * <h3>Index Structure Overview</h3>
- *
- * <div>
- *
- * <p>Each segment index maintains the following:
- *
- * <ul>
- *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat Segment info}. This
- *       contains metadata about a segment, such as the number of documents, what files it uses, and
- *       information about how the segment is sorted
- *   <li>{@link org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat Field names}. This
- *       contains metadata about the set of named fields used in the index.
- *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Stored Field values}.
- *       This contains, for each document, a list of attribute-value pairs, where the attributes are
- *       field names. These are used to store auxiliary information about the document, such as its
- *       title, url, or an identifier to access a database. The set of stored fields are what is
- *       returned for each hit when searching. This is keyed by document number.
- *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat Term dictionary}. A
- *       dictionary containing all of the terms used in all of the indexed fields of all of the
- *       documents. The dictionary also contains the number of documents which contain the term, and
- *       pointers to the term's frequency and proximity data.
- *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat Term Frequency data}. For
- *       each term in the dictionary, the numbers of all the documents that contain that term, and
- *       the frequency of the term in that document, unless frequencies are omitted ({@link
- *       org.apache.lucene.index.IndexOptions#DOCS IndexOptions.DOCS})
- *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat Term Proximity data}. For
- *       each term in the dictionary, the positions that the term occurs in each document. Note that
- *       this will not exist if all fields in all documents omit position data.
- *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90NormsFormat Normalization factors}. For
- *       each field in each document, a value is stored that is multiplied into the score for hits
- *       on that field.
- *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vectors}. For each
- *       field in each document, the term vector (sometimes called document vector) may be stored. A
- *       term vector consists of term text and term frequency. To add Term Vectors to your index see
- *       the {@link org.apache.lucene.document.Field Field} constructors
- *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat Per-document values}. Like
- *       stored values, these are also keyed by document number, but are generally intended to be
- *       loaded into main memory for fast access. Whereas stored values are generally intended for
- *       summary results from searches, per-document values are useful for things like scoring
- *       factors.
- *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat Live documents}. An
- *       optional file indicating which documents are live.
- *   <li>{@link org.apache.lucene.codecs.lucene90.Lucene90PointsFormat Point values}. Optional pair
- *       of files, recording dimensionally indexed fields, to enable fast numeric range filtering
- *       and large numeric values like BigInteger and BigDecimal (1D) and geographic shape
- *       intersection (2D, 3D).
- *   <li>{@link org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat Vector values}. The
- *       vector format stores numeric vectors in a format optimized for random access and
- *       computation, supporting high-dimensional nearest-neighbor search.
- * </ul>
- *
- * <p>Details on each of these are provided in their linked pages. </div> <a id="File_Naming"></a>
- *
- * <h3>File Naming</h3>
- *
- * <div>
- *
- * <p>All files belonging to a segment have the same name with varying extensions. The extensions
- * correspond to the different file formats described below. When using the Compound File format
- * (default for small segments) these files (except for the Segment info file, the Lock file, and
- * Deleted documents file) are collapsed into a single .cfs file (see below for details)
- *
- * <p>Typically, all segments in an index are stored in a single directory, although this is not
- * required.
- *
- * <p>File names are never re-used. That is, when any file is saved to the Directory it is given a
- * never before used filename. This is achieved using a simple generations approach. For example,
- * the first segments file is segments_1, then segments_2, etc. The generation is a sequential long
- * integer represented in alpha-numeric (base 36) form. </div> <a id="file-names"></a>
- *
- * <h3>Summary of File Extensions</h3>
- *
- * <div>
- *
- * <p>The following table summarizes the names and extensions of the files in Lucene:
- *
- * <table class="padding4" style="border-spacing: 1px; border-collapse: separate">
- * <caption>lucene filenames by extension</caption>
- * <tr>
- * <th>Name</th>
- * <th>Extension</th>
- * <th>Brief Description</th>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.index.SegmentInfos Segments File}</td>
- * <td>segments_N</td>
- * <td>Stores information about a commit point</td>
- * </tr>
- * <tr>
- * <td><a href="#Lock_File">Lock File</a></td>
- * <td>write.lock</td>
- * <td>The Write lock prevents multiple IndexWriters from writing to the same
- * file.</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat Segment Info}</td>
- * <td>.si</td>
- * <td>Stores metadata about a segment</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90CompoundFormat Compound File}</td>
- * <td>.cfs, .cfe</td>
- * <td>An optional "virtual" file consisting of all the other index files for
- * systems that frequently run out of file handles.</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat Fields}</td>
- * <td>.fnm</td>
- * <td>Stores information about the fields</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Field Index}</td>
- * <td>.fdx</td>
- * <td>Contains pointers to field data</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Field Data}</td>
- * <td>.fdt</td>
- * <td>The stored fields for documents</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat Term Dictionary}</td>
- * <td>.tim</td>
- * <td>The term dictionary, stores term info</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat Term Index}</td>
- * <td>.tip</td>
- * <td>The index into the Term Dictionary</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat Frequencies}</td>
- * <td>.doc</td>
- * <td>Contains the list of docs which contain each term along with frequency</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat Positions}</td>
- * <td>.pos</td>
- * <td>Stores position information about where a term occurs in the index</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat Payloads}</td>
- * <td>.pay</td>
- * <td>Stores additional per-position metadata information such as character offsets and user payloads</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90NormsFormat Norms}</td>
- * <td>.nvd, .nvm</td>
- * <td>Encodes length and boost factors for docs and fields</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat Per-Document Values}</td>
- * <td>.dvd, .dvm</td>
- * <td>Encodes additional scoring factors or other per-document information.</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vector Index}</td>
- * <td>.tvx</td>
- * <td>Stores offset into the document data file</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vector Data}</td>
- * <td>.tvd</td>
- * <td>Contains term vector data.</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat Live Documents}</td>
- * <td>.liv</td>
- * <td>Info about what documents are live</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90PointsFormat Point values}</td>
- * <td>.dii, .dim</td>
- * <td>Holds indexed points</td>
- * </tr>
- * <tr>
- * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat Vector values}</td>
- * <td>.vec, .vem, .veq, vex</td>
- * <td>Holds indexed vectors; <code>.vec</code> files contain the raw vector data,
- * <code>.vem</code> the vector metadata, <code>.veq</code> the quantized vector data, and <code>.vex</code> the
- * hnsw graph data.</td>
- * </tr>
- * </table>
- *
- * </div> <a id="Lock_File"></a>
- *
- * <h3>Lock File</h3>
- *
- * The write lock, which is stored in the index directory by default, is named "write.lock". If the
- * lock directory is different from the index directory then the write lock will be named
- * "XXXX-write.lock" where XXXX is a unique prefix derived from the full path to the index
- * directory. When this file is present, a writer is currently modifying the index (adding or
- * removing documents). This lock file ensures that only one writer is modifying the index at a
- * time. <a id="History"></a>
- *
- * <h3>History</h3>
- *
- * <p>Compatibility notes are provided in this document, describing how file formats have changed
- * from prior versions:
- *
- * <ul>
- *   <li>In version 2.1, the file format was changed to allow lock-less commits (ie, no more commit
- *       lock). The change is fully backwards compatible: you can open a pre-2.1 index for searching
- *       or adding/deleting of docs. When the new segments file is saved (committed), it will be
- *       written in the new file format (meaning no specific "upgrade" process is needed). But note
- *       that once a commit has occurred, pre-2.1 Lucene will not be able to read the index.
- *   <li>In version 2.3, the file format was changed to allow segments to share a single set of doc
- *       store (vectors &amp; stored fields) files. This allows for faster indexing in certain
- *       cases. The change is fully backwards compatible (in the same way as the lock-less commits
- *       change in 2.1).
- *   <li>In version 2.4, Strings are now written as true UTF-8 byte sequence, not Java's modified
- *       UTF-8. See <a href="http://issues.apache.org/jira/browse/LUCENE-510">LUCENE-510</a> for
- *       details.
- *   <li>In version 2.9, an optional opaque Map&lt;String,String&gt; CommitUserData may be passed to
- *       IndexWriter's commit methods (and later retrieved), which is recorded in the segments_N
- *       file. See <a href="http://issues.apache.org/jira/browse/LUCENE-1382">LUCENE-1382</a> for
- *       details. Also, diagnostics were added to each segment written recording details about why
- *       it was written (due to flush, merge; which OS/JRE was used; etc.). See issue <a
- *       href="http://issues.apache.org/jira/browse/LUCENE-1654">LUCENE-1654</a> for details.
- *   <li>In version 3.0, compressed fields are no longer written to the index (they can still be
- *       read, but on merge the new segment will write them, uncompressed). See issue <a
- *       href="http://issues.apache.org/jira/browse/LUCENE-1960">LUCENE-1960</a> for details.
- *   <li>In version 3.1, segments records the code version that created them. See <a
- *       href="http://issues.apache.org/jira/browse/LUCENE-2720">LUCENE-2720</a> for details.
- *       Additionally segments track explicitly whether or not they have term vectors. See <a
- *       href="http://issues.apache.org/jira/browse/LUCENE-2811">LUCENE-2811</a> for details.
- *   <li>In version 3.2, numeric fields are written as natively to stored fields file, previously
- *       they were stored in text format only.
- *   <li>In version 3.4, fields can omit position data while still indexing term frequencies.
- *   <li>In version 4.0, the format of the inverted index became extensible via the {@link
- *       org.apache.lucene.codecs.Codec Codec} api. Fast per-document storage ({@code DocValues})
- *       was introduced. Normalization factors need no longer be a single byte, they can be any
- *       {@link org.apache.lucene.index.NumericDocValues NumericDocValues}. Terms need not be
- *       unicode strings, they can be any byte sequence. Term offsets can optionally be indexed into
- *       the postings lists. Payloads can be stored in the term vectors.
- *   <li>In version 4.1, the format of the postings list changed to use either of FOR compression or
- *       variable-byte encoding, depending upon the frequency of the term. Terms appearing only once
- *       were changed to inline directly into the term dictionary. Stored fields are compressed by
- *       default.
- *   <li>In version 4.2, term vectors are compressed by default. DocValues has a new multi-valued
- *       type (SortedSet), that can be used for faceting/grouping/joining on multi-valued fields.
- *   <li>In version 4.5, DocValues were extended to explicitly represent missing values.
- *   <li>In version 4.6, FieldInfos were extended to support per-field DocValues generation, to
- *       allow updating NumericDocValues fields.
- *   <li>In version 4.8, checksum footers were added to the end of each index file for improved data
- *       integrity. Specifically, the last 8 bytes of every index file contain the zlib-crc32
- *       checksum of the file.
- *   <li>In version 4.9, DocValues has a new multi-valued numeric type (SortedNumeric) that is
- *       suitable for faceting/sorting/analytics.
- *   <li>In version 5.4, DocValues have been improved to store more information on disk: addresses
- *       for binary fields and ord indexes for multi-valued fields.
- *   <li>In version 6.0, Points were added, for multi-dimensional range/distance search.
- *   <li>In version 6.2, new Segment info format that reads/writes the index sort, to support index
- *       sorting.
- *   <li>In version 7.0, DocValues have been improved to better support sparse doc values thanks to
- *       an iterator API.
- *   <li>In version 8.0, postings have been enhanced to record, for each block of doc ids, the (term
- *       freq, normalization factor) pairs that may trigger the maximum score of the block. This
- *       information is recorded alongside skip data in order to be able to skip blocks of doc ids
- *       if they may not produce high enough scores. Additionally doc values and norms has been
- *       extended with jump-tables to make access O(1) instead of O(n), where n is the number of
- *       elements to skip when advancing in the data.
- *   <li>In version 8.4, postings, positions, offsets and payload lengths have move to a more
- *       performant encoding that is vectorized.
- *   <li>In version 8.6, index sort serialization is delegated to the sorts themselves, to allow
- *       user-defined sorts to be used
- *   <li>In version 8.7, stored fields compression became adaptive to better handle documents with
- *       smaller stored fields.
- *   <li>In version 9.0, vector-valued fields were added.
- *   <li>In version 9.1, vector-valued fields were modified to add a graph hierarchy.
- *   <li>In version 9.2, docs of vector-valued fields were moved from .vem to .vec and encoded by
- *       IndexDISI. ordToDoc mappings was added to .vem.
- *   <li>In version 9.5, HNSW graph connections were changed to be delta-encoded with vints.
- *       Additionally, metadata file size improvements were made by delta-encoding nodes by graph
- *       layer and not writing the node ids for the zeroth layer.
- *   <li>In version 9.9, Vector scalar quantization support was added. Allowing the HNSW vector
- *       format to utilize int8 quantized vectors for float32 vector search.
- * </ul>
- *
- * <a id="Limitations"></a>
- *
- * <h3>Limitations</h3>
- *
- * <div>
- *
- * <p>Lucene uses a Java <code>int</code> to refer to document numbers, and the index file format
- * uses an <code>Int32</code> on-disk to store document numbers. This is a limitation of both the
- * index file format and the current implementation. Eventually these should be replaced with either
- * <code>UInt64</code> values, or better yet, {@link org.apache.lucene.store.DataOutput#writeVInt
- * VInt} values which have no limit. </div>
- */
+/** Lucene 9.9 file format. */
 package org.apache.lucene.codecs.lucene99;

lucene/core/src/java/org/apache/lucene/index/CheckIndex.java

@@ -3302,17 +3302,17 @@ public final class CheckIndex implements Closeable {
       if (skipper.maxDocID(0) == NO_MORE_DOCS) {
         break;
       }
+      if (skipper.minDocID(0) < doc) {
+        throw new CheckIndexException(
+            "skipper dv iterator for field: "
+                + fieldName
+                + " reports wrong minDocID, got "
+                + skipper.minDocID(0)
+                + " < "
+                + doc);
+      }
       int levels = skipper.numLevels();
       for (int level = 0; level < levels; level++) {
-        if (skipper.minDocID(level) < doc) {
-          throw new CheckIndexException(
-              "skipper dv iterator for field: "
-                  + fieldName
-                  + " reports wrong minDocID, got "
-                  + skipper.minDocID(level)
-                  + " < "
-                  + doc);
-        }
         if (skipper.minDocID(level) > skipper.maxDocID(level)) {
           throw new CheckIndexException(
               "skipper dv iterator for field: "

lucene/core/src/java/org/apache/lucene/index/DocumentsWriter.java

@@ -430,10 +430,16 @@ final class DocumentsWriter implements Closeable, Accountable {
       }
       flushingDWPT = flushControl.doAfterDocument(dwpt);
     } finally {
-      if (dwpt.isFlushPending() || dwpt.isAborted()) {
-        dwpt.unlock();
-      } else {
-        perThreadPool.marksAsFreeAndUnlock(dwpt);
+      // If a flush is occurring, we don't want to allow this dwpt to be reused
+      // If it is aborted, we shouldn't allow it to be reused
+      // If the deleteQueue is advanced, this means the maximum seqNo has been set and it cannot be
+      // reused
+      synchronized (flushControl) {
+        if (dwpt.isFlushPending() || dwpt.isAborted() || dwpt.isQueueAdvanced()) {
+          dwpt.unlock();
+        } else {
+          perThreadPool.marksAsFreeAndUnlock(dwpt);
+        }
       }
       assert dwpt.isHeldByCurrentThread() == false : "we didn't release the dwpt even on abort";
     }

lucene/core/src/java/org/apache/lucene/index/DocumentsWriterDeleteQueue.java

@@ -636,7 +636,7 @@ final class DocumentsWriterDeleteQueue implements Accountable, Closeable {
   }
 
   /** Returns <code>true</code> if it was advanced. */
-  boolean isAdvanced() {
+  synchronized boolean isAdvanced() {
     return advanced;
   }
 }

lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThread.java

@@ -718,6 +718,10 @@ final class DocumentsWriterPerThread implements Accountable, Lock {
     return flushPending.get() == Boolean.TRUE;
   }
 
+  boolean isQueueAdvanced() {
+    return deleteQueue.isAdvanced();
+  }
+
   /** Sets this DWPT as flush pending. This can only be set once. */
   void setFlushPending() {
     flushPending.set(Boolean.TRUE);

lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThreadPool.java

@@ -138,6 +138,15 @@ final class DocumentsWriterPerThreadPool implements Iterable<DocumentsWriterPerT
 
   void marksAsFreeAndUnlock(DocumentsWriterPerThread state) {
     final long ramBytesUsed = state.ramBytesUsed();
+    assert state.isFlushPending() == false
+            && state.isAborted() == false
+            && state.isQueueAdvanced() == false
+        : "DWPT has pending flush: "
+            + state.isFlushPending()
+            + " aborted="
+            + state.isAborted()
+            + " queueAdvanced="
+            + state.isQueueAdvanced();
     assert contains(state)
         : "we tried to add a DWPT back to the pool but the pool doesn't know about this DWPT";
     freeList.addAndUnlock(state, ramBytesUsed);

lucene/core/src/java/org/apache/lucene/index/LogMergePolicy.java

@@ -90,6 +90,12 @@ public abstract class LogMergePolicy extends MergePolicy {
   /** If true, we pro-rate a segment's size by the percentage of non-deleted documents. */
   protected boolean calibrateSizeByDeletes = true;
 
+  /**
+   * Target search concurrency. This merge policy will avoid creating segments that have more than
+   * {@code maxDoc / targetSearchConcurrency} documents.
+   */
+  protected int targetSearchConcurrency = 1;
+
   /** Sole constructor. (For invocation by subclass constructors, typically implicit.) */
   public LogMergePolicy() {
     super(DEFAULT_NO_CFS_RATIO, MergePolicy.DEFAULT_MAX_CFS_SEGMENT_SIZE);
@@ -131,6 +137,28 @@ public abstract class LogMergePolicy extends MergePolicy {
     return calibrateSizeByDeletes;
   }
 
+  /**
+   * Sets the target search concurrency. This prevents creating segments that are bigger than
+   * maxDoc/targetSearchConcurrency, which in turn makes the work parallelizable into
+   * targetSearchConcurrency slices of similar doc counts.
+   *
+   * <p><b>NOTE:</b> Configuring a value greater than 1 will increase the number of segments in the
+   * index linearly with the value of {@code targetSearchConcurrency} and also increase write
+   * amplification.
+   */
+  public void setTargetSearchConcurrency(int targetSearchConcurrency) {
+    if (targetSearchConcurrency < 1) {
+      throw new IllegalArgumentException(
+          "targetSearchConcurrency must be >= 1 (got " + targetSearchConcurrency + ")");
+    }
+    this.targetSearchConcurrency = targetSearchConcurrency;
+  }
+
+  /** Returns the target search concurrency. */
+  public int getTargetSearchConcurrency() {
+    return targetSearchConcurrency;
+  }
+
   /**
    * Return the number of documents in the provided {@link SegmentCommitInfo}, pro-rated by
    * percentage of non-deleted documents if {@link #setCalibrateSizeByDeletes} is set.
@@ -484,8 +512,10 @@ public abstract class LogMergePolicy extends MergePolicy {
 
     final Set<SegmentCommitInfo> mergingSegments = mergeContext.getMergingSegments();
 
+    int totalDocCount = 0;
     for (int i = 0; i < numSegments; i++) {
       final SegmentCommitInfo info = infos.info(i);
+      totalDocCount += sizeDocs(info, mergeContext);
       long size = size(info, mergeContext);
 
       // Floor tiny segments
@@ -575,6 +605,9 @@ public abstract class LogMergePolicy extends MergePolicy {
             mergeContext);
       }
 
+      final int maxMergeDocs =
+          Math.min(this.maxMergeDocs, Math.ceilDiv(totalDocCount, targetSearchConcurrency));
+
       // Finally, record all merges that are viable at this level:
       int end = start + mergeFactor;
       while (end <= 1 + upto) {

lucene/core/src/java/org/apache/lucene/index/SoftDeletesDirectoryReaderWrapper.java

@@ -141,6 +141,9 @@ public final class SoftDeletesDirectoryReaderWrapper extends FilterDirectoryRead
       bits.set(0, reader.maxDoc());
     }
     int numSoftDeletes = PendingSoftDeletes.applySoftDeletes(iterator, bits);
+    if (numSoftDeletes == 0) {
+      return reader;
+    }
     int numDeletes = reader.numDeletedDocs() + numSoftDeletes;
     int numDocs = reader.maxDoc() - numDeletes;
     assert assertDocCounts(numDocs, numSoftDeletes, reader);

lucene/core/src/java/org/apache/lucene/index/TieredMergePolicy.java

@@ -93,6 +93,7 @@ public class TieredMergePolicy extends MergePolicy {
   private double segsPerTier = 10.0;
   private double forceMergeDeletesPctAllowed = 10.0;
   private double deletesPctAllowed = 20.0;
+  private int targetSearchConcurrency = 1;
 
   /** Sole constructor, setting all settings to their defaults. */
   public TieredMergePolicy() {
@@ -257,6 +258,26 @@ public class TieredMergePolicy extends MergePolicy {
     return segsPerTier;
   }
 
+  /**
+   * Sets the target search concurrency. This prevents creating segments that are bigger than
+   * maxDoc/targetSearchConcurrency, which in turn makes the work parallelizable into
+   * targetSearchConcurrency slices of similar doc counts. It also makes merging less aggressive, as
+   * higher values result in indices that do less merging and have more segments
+   */
+  public TieredMergePolicy setTargetSearchConcurrency(int targetSearchConcurrency) {
+    if (targetSearchConcurrency < 1) {
+      throw new IllegalArgumentException(
+          "targetSearchConcurrency must be >= 1 (got " + targetSearchConcurrency + ")");
+    }
+    this.targetSearchConcurrency = targetSearchConcurrency;
+    return this;
+  }
+
+  /** Returns the target search concurrency. */
+  public int getTargetSearchConcurrency() {
+    return targetSearchConcurrency;
+  }
+
   private static class SegmentSizeAndDocs {
     private final SegmentCommitInfo segInfo;
     /// Size of the segment in bytes, pro-rated by the number of live documents.
@@ -371,31 +392,40 @@ public class TieredMergePolicy extends MergePolicy {
     // If we have too-large segments, grace them out of the maximum segment count
     // If we're above certain thresholds of deleted docs, we can merge very large segments.
     int tooBigCount = 0;
+    // We relax merging for the bigger segments for concurrency reasons, as we want to have several
+    // segments on the highest tier without over-merging on the lower tiers.
+    int concurrencyCount = 0;
     iter = sortedInfos.iterator();
 
+    double allowedSegCount = 0;
+
     // remove large segments from consideration under two conditions.
     // 1> Overall percent deleted docs relatively small and this segment is larger than 50%
     // maxSegSize
     // 2> overall percent deleted docs large and this segment is large and has few deleted docs
-
     while (iter.hasNext()) {
       SegmentSizeAndDocs segSizeDocs = iter.next();
       double segDelPct = 100 * (double) segSizeDocs.delCount / (double) segSizeDocs.maxDoc;
       if (segSizeDocs.sizeInBytes > maxMergedSegmentBytes / 2
           && (totalDelPct <= deletesPctAllowed || segDelPct <= deletesPctAllowed)) {
         iter.remove();
-        tooBigCount++; // Just for reporting purposes.
+        tooBigCount++;
         totIndexBytes -= segSizeDocs.sizeInBytes;
         allowedDelCount -= segSizeDocs.delCount;
+      } else if (concurrencyCount + tooBigCount < targetSearchConcurrency - 1) {
+        // Make sure we count a whole segment for the first targetSearchConcurrency-1 segments to
+        // avoid over merging on the lower levels.
+        concurrencyCount++;
+        allowedSegCount++;
+        totIndexBytes -= segSizeDocs.sizeInBytes;
       }
     }
     allowedDelCount = Math.max(0, allowedDelCount);
 
     final int mergeFactor = (int) Math.min(maxMergeAtOnce, segsPerTier);
-    // Compute max allowed segments in the index
+    // Compute max allowed segments for the remainder of the index
     long levelSize = Math.max(minSegmentBytes, floorSegmentBytes);
     long bytesLeft = totIndexBytes;
-    double allowedSegCount = 0;
     while (true) {
       final double segCountLevel = bytesLeft / (double) levelSize;
       if (segCountLevel < segsPerTier || levelSize == maxMergedSegmentBytes) {
@@ -408,7 +438,8 @@ public class TieredMergePolicy extends MergePolicy {
     }
     // allowedSegCount may occasionally be less than segsPerTier
     // if segment sizes are below the floor size
-    allowedSegCount = Math.max(allowedSegCount, segsPerTier);
+    allowedSegCount = Math.max(allowedSegCount, Math.max(segsPerTier, targetSearchConcurrency));
+    int allowedDocCount = getMaxAllowedDocs(totalMaxDoc, totalDelDocs);
 
     if (verbose(mergeContext) && tooBigCount > 0) {
       message(
@@ -419,7 +450,11 @@ public class TieredMergePolicy extends MergePolicy {
               + " (eligible count="
               + sortedInfos.size()
               + ") tooBigCount= "
-              + tooBigCount,
+              + tooBigCount
+              + "  allowedDocCount="
+              + allowedDocCount
+              + " vs doc count="
+              + infos.totalMaxDoc(),
           mergeContext);
     }
     return doFindMerges(
@@ -428,6 +463,7 @@ public class TieredMergePolicy extends MergePolicy {
         mergeFactor,
         (int) allowedSegCount,
         allowedDelCount,
+        allowedDocCount,
         MERGE_TYPE.NATURAL,
         mergeContext,
         mergingBytes >= maxMergedSegmentBytes);
@@ -439,6 +475,7 @@ public class TieredMergePolicy extends MergePolicy {
       final int mergeFactor,
       final int allowedSegCount,
       final int allowedDelCount,
+      final int allowedDocCount,
       final MERGE_TYPE mergeType,
       MergeContext mergeContext,
       boolean maxMergeIsRunning)
@@ -522,16 +559,23 @@ public class TieredMergePolicy extends MergePolicy {
         final List<SegmentCommitInfo> candidate = new ArrayList<>();
         boolean hitTooLarge = false;
         long bytesThisMerge = 0;
+        long docCountThisMerge = 0;
         for (int idx = startIdx;
             idx < sortedEligible.size()
                 && candidate.size() < mergeFactor
-                && bytesThisMerge < maxMergedSegmentBytes;
+                && bytesThisMerge < maxMergedSegmentBytes
+                && (bytesThisMerge < floorSegmentBytes || docCountThisMerge <= allowedDocCount);
             idx++) {
           final SegmentSizeAndDocs segSizeDocs = sortedEligible.get(idx);
           final long segBytes = segSizeDocs.sizeInBytes;
-
-          if (totAfterMergeBytes + segBytes > maxMergedSegmentBytes) {
-            hitTooLarge = true;
+          int segDocCount = segSizeDocs.maxDoc - segSizeDocs.delCount;
+          if (totAfterMergeBytes + segBytes > maxMergedSegmentBytes
+              || (totAfterMergeBytes > floorSegmentBytes
+                  && docCountThisMerge + segDocCount > allowedDocCount)) {
+            // Only set hitTooLarge when reaching the maximum byte size, as this will create
+            // segments of the maximum size which will no longer be eligible for merging for a long
+            // time (until they accumulate enough deletes).
+            hitTooLarge |= totAfterMergeBytes + segBytes > maxMergedSegmentBytes;
             if (candidate.size() == 0) {
               // We should never have something coming in that _cannot_ be merged, so handle
               // singleton merges
@@ -548,6 +592,7 @@ public class TieredMergePolicy extends MergePolicy {
           }
           candidate.add(segSizeDocs.segInfo);
           bytesThisMerge += segBytes;
+          docCountThisMerge += segDocCount;
           totAfterMergeBytes += segBytes;
         }
 
@@ -916,14 +961,13 @@ public class TieredMergePolicy extends MergePolicy {
     final Set<SegmentCommitInfo> merging = mergeContext.getMergingSegments();
 
     boolean haveWork = false;
+    int totalDelCount = 0;
     for (SegmentCommitInfo info : infos) {
       int delCount = mergeContext.numDeletesToMerge(info);
       assert assertDelCount(delCount, info);
+      totalDelCount += delCount;
       double pctDeletes = 100. * ((double) delCount) / info.info.maxDoc();
-      if (pctDeletes > forceMergeDeletesPctAllowed && !merging.contains(info)) {
-        haveWork = true;
-        break;
-      }
+      haveWork = haveWork || (pctDeletes > forceMergeDeletesPctAllowed && !merging.contains(info));
     }
 
     if (haveWork == false) {
@@ -950,11 +994,16 @@ public class TieredMergePolicy extends MergePolicy {
         Integer.MAX_VALUE,
         Integer.MAX_VALUE,
         0,
+        getMaxAllowedDocs(infos.totalMaxDoc(), totalDelCount),
         MERGE_TYPE.FORCE_MERGE_DELETES,
         mergeContext,
         false);
   }
 
+  int getMaxAllowedDocs(int totalMaxDoc, int totalDelDocs) {
+    return Math.ceilDiv(totalMaxDoc - totalDelDocs, targetSearchConcurrency);
+  }
+
   private long floorSize(long bytes) {
     return Math.max(floorSegmentBytes, bytes);
   }
@@ -969,7 +1018,8 @@ public class TieredMergePolicy extends MergePolicy {
     sb.append("segmentsPerTier=").append(segsPerTier).append(", ");
     sb.append("maxCFSSegmentSizeMB=").append(getMaxCFSSegmentSizeMB()).append(", ");
     sb.append("noCFSRatio=").append(noCFSRatio).append(", ");
-    sb.append("deletesPctAllowed=").append(deletesPctAllowed);
+    sb.append("deletesPctAllowed=").append(deletesPctAllowed).append(", ");
+    sb.append("targetSearchConcurrency=").append(targetSearchConcurrency);
     return sb.toString();
   }
 }

lucene/core/src/java/org/apache/lucene/index/VectorSimilarityFunction.java

@@ -66,10 +66,7 @@ public enum VectorSimilarityFunction {
    * vectors to unit length, and instead use {@link VectorSimilarityFunction#DOT_PRODUCT}. You
    * should only use this function if you need to preserve the original vectors and cannot normalize
    * them in advance. The similarity score is normalised to assure it is positive.
-   *
-   * @deprecated Use MAXIMUM_INNER_PRODUCT or DOT_PRODUCT instead
    */
-  @Deprecated
   COSINE {
     @Override
     public float compare(float[] v1, float[] v2) {

lucene/core/src/java/org/apache/lucene/internal/hppc/IntLongHashMap.java

@@ -0,0 +1,834 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.lucene.internal.hppc;
+
+import static org.apache.lucene.internal.hppc.HashContainers.*;
+
+import java.util.Arrays;
+import java.util.Iterator;
+import org.apache.lucene.util.Accountable;
+import org.apache.lucene.util.RamUsageEstimator;
+
+/**
+ * A hash map of <code>int</code> to <code>long</code>, implemented using open addressing with
+ * linear probing for collision resolution.
+ *
+ * <p>Mostly forked and trimmed from com.carrotsearch.hppc.IntLongHashMap
+ *
+ * <p>github: https://github.com/carrotsearch/hppc release 0.10.0
+ *
+ * @lucene.internal
+ */
+public class IntLongHashMap
+    implements Iterable<IntLongHashMap.IntLongCursor>, Accountable, Cloneable {
+
+  private static final long BASE_RAM_BYTES_USED =
+      RamUsageEstimator.shallowSizeOfInstance(IntLongHashMap.class);
+
+  /** The array holding keys. */
+  public int[] keys;
+
+  /** The array holding values. */
+  public long[] values;
+
+  /**
+   * The number of stored keys (assigned key slots), excluding the special "empty" key, if any (use
+   * {@link #size()} instead).
+   *
+   * @see #size()
+   */
+  protected int assigned;
+
+  /** Mask for slot scans in {@link #keys}. */
+  protected int mask;
+
+  /** Expand (rehash) {@link #keys} when {@link #assigned} hits this value. */
+  protected int resizeAt;
+
+  /** Special treatment for the "empty slot" key marker. */
+  protected boolean hasEmptyKey;
+
+  /** The load factor for {@link #keys}. */
+  protected double loadFactor;
+
+  /** Seed used to ensure the hash iteration order is different from an iteration to another. */
+  protected int iterationSeed;
+
+  /** New instance with sane defaults. */
+  public IntLongHashMap() {
+    this(DEFAULT_EXPECTED_ELEMENTS);
+  }
+
+  /**
+   * New instance with sane defaults.
+   *
+   * @param expectedElements The expected number of elements guaranteed not to cause buffer
+   *     expansion (inclusive).
+   */
+  public IntLongHashMap(int expectedElements) {
+    this(expectedElements, DEFAULT_LOAD_FACTOR);
+  }
+
+  /**
+   * New instance with the provided defaults.
+   *
+   * @param expectedElements The expected number of elements guaranteed not to cause a rehash
+   *     (inclusive).
+   * @param loadFactor The load factor for internal buffers. Insane load factors (zero, full
+   *     capacity) are rejected by {@link #verifyLoadFactor(double)}.
+   */
+  public IntLongHashMap(int expectedElements, double loadFactor) {
+    this.loadFactor = verifyLoadFactor(loadFactor);
+    iterationSeed = ITERATION_SEED.incrementAndGet();
+    ensureCapacity(expectedElements);
+  }
+
+  /** Create a hash map from all key-value pairs of another container. */
+  public IntLongHashMap(IntLongHashMap container) {
+    this(container.size());
+    putAll(container);
+  }
+
+  public long put(int key, long value) {
+    assert assigned < mask + 1;
+
+    final int mask = this.mask;
+    if (((key) == 0)) {
+      long previousValue = hasEmptyKey ? values[mask + 1] : 0L;
+      hasEmptyKey = true;
+      values[mask + 1] = value;
+      return previousValue;
+    } else {
+      final int[] keys = this.keys;
+      int slot = hashKey(key) & mask;
+
+      int existing;
+      while (!((existing = keys[slot]) == 0)) {
+        if (((key) == (existing))) {
+          final long previousValue = values[slot];
+          values[slot] = value;
+          return previousValue;
+        }
+        slot = (slot + 1) & mask;
+      }
+
+      if (assigned == resizeAt) {
+        allocateThenInsertThenRehash(slot, key, value);
+      } else {
+        keys[slot] = key;
+        values[slot] = value;
+      }
+
+      assigned++;
+      return 0L;
+    }
+  }
+
+  /**
+   * If the specified key is not already associated with a value, associates it with the given
+   * value.
+   *
+   * @return {@code true} if {@code key} did not exist and {@code value} was placed in the map,
+   *     {@code false} otherwise.
+   */
+  public boolean putIfAbsent(int key, long value) {
+    int keyIndex = indexOf(key);
+    if (indexExists(keyIndex)) {
+      return false;
+    } else {
+      indexInsert(keyIndex, key, value);
+      return true;
+    }
+  }
+
+  /** Puts all key/value pairs from a given iterable into this map. */
+  public int putAll(Iterable<? extends IntLongCursor> iterable) {
+    final int count = size();
+    for (IntLongCursor c : iterable) {
+      put(c.key, c.value);
+    }
+    return size() - count;
+  }
+
+  /**
+   * If <code>key</code> exists, <code>putValue</code> is inserted into the map, otherwise any
+   * existing value is incremented by <code>additionValue</code>.
+   *
+   * @param key The key of the value to adjust.
+   * @param putValue The value to put if <code>key</code> does not exist.
+   * @param incrementValue The value to add to the existing value if <code>key</code> exists.
+   * @return Returns the current value associated with <code>key</code> (after changes).
+   */
+  public long putOrAdd(int key, long putValue, long incrementValue) {
+    assert assigned < mask + 1;
+
+    int keyIndex = indexOf(key);
+    if (indexExists(keyIndex)) {
+      putValue = values[keyIndex] + incrementValue;
+      indexReplace(keyIndex, putValue);
+    } else {
+      indexInsert(keyIndex, key, putValue);
+    }
+    return putValue;
+  }
+
+  /**
+   * Adds <code>incrementValue</code> to any existing value for the given <code>key</code> or
+   * inserts <code>incrementValue</code> if <code>key</code> did not previously exist.
+   *
+   * @param key The key of the value to adjust.
+   * @param incrementValue The value to put or add to the existing value if <code>key</code> exists.
+   * @return Returns the current value associated with <code>key</code> (after changes).
+   */
+  public long addTo(int key, long incrementValue) {
+    return putOrAdd(key, incrementValue, incrementValue);
+  }
+
+  /**
+   * Remove all values at the given key. The default value for the key type is returned if the value
+   * does not exist in the map.
+   */
+  public long remove(int key) {
+    final int mask = this.mask;
+    if (((key) == 0)) {
+      if (!hasEmptyKey) {
+        return 0L;
+      }
+      hasEmptyKey = false;
+      long previousValue = values[mask + 1];
+      values[mask + 1] = 0L;
+      return previousValue;
+    } else {
+      final int[] keys = this.keys;
+      int slot = hashKey(key) & mask;
+
+      int existing;
+      while (!((existing = keys[slot]) == 0)) {
+        if (((key) == (existing))) {
+          final long previousValue = values[slot];
+          shiftConflictingKeys(slot);
+          return previousValue;
+        }
+        slot = (slot + 1) & mask;
+      }
+
+      return 0L;
+    }
+  }
+
+  public long get(int key) {
+    if (((key) == 0)) {
+      return hasEmptyKey ? values[mask + 1] : 0L;
+    } else {
+      final int[] keys = this.keys;
+      final int mask = this.mask;
+      int slot = hashKey(key) & mask;
+
+      int existing;
+      while (!((existing = keys[slot]) == 0)) {
+        if (((key) == (existing))) {
+          return values[slot];
+        }
+        slot = (slot + 1) & mask;
+      }
+
+      return 0L;
+    }
+  }
+
+  public long getOrDefault(int key, long defaultValue) {
+    if (((key) == 0)) {
+      return hasEmptyKey ? values[mask + 1] : defaultValue;
+    } else {
+      final int[] keys = this.keys;
+      final int mask = this.mask;
+      int slot = hashKey(key) & mask;
+
+      int existing;
+      while (!((existing = keys[slot]) == 0)) {
+        if (((key) == (existing))) {
+          return values[slot];
+        }
+        slot = (slot + 1) & mask;
+      }
+
+      return defaultValue;
+    }
+  }
+
+  public boolean containsKey(int key) {
+    if (((key) == 0)) {
+      return hasEmptyKey;
+    } else {
+      final int[] keys = this.keys;
+      final int mask = this.mask;
+      int slot = hashKey(key) & mask;
+
+      int existing;
+      while (!((existing = keys[slot]) == 0)) {
+        if (((key) == (existing))) {
+          return true;
+        }
+        slot = (slot + 1) & mask;
+      }
+
+      return false;
+    }
+  }
+
+  public int indexOf(int key) {
+    final int mask = this.mask;
+    if (((key) == 0)) {
+      return hasEmptyKey ? mask + 1 : ~(mask + 1);
+    } else {
+      final int[] keys = this.keys;
+      int slot = hashKey(key) & mask;
+
+      int existing;
+      while (!((existing = keys[slot]) == 0)) {
+        if (((key) == (existing))) {
+          return slot;
+        }
+        slot = (slot + 1) & mask;
+      }
+
+      return ~slot;
+    }
+  }
+
+  public boolean indexExists(int index) {
+    assert index < 0 || (index >= 0 && index <= mask) || (index == mask + 1 && hasEmptyKey);
+
+    return index >= 0;
+  }
+
+  public long indexGet(int index) {
+    assert index >= 0 : "The index must point at an existing key.";
+    assert index <= mask || (index == mask + 1 && hasEmptyKey);
+
+    return values[index];
+  }
+
+  public long indexReplace(int index, long newValue) {
+    assert index >= 0 : "The index must point at an existing key.";
+    assert index <= mask || (index == mask + 1 && hasEmptyKey);
+
+    long previousValue = values[index];
+    values[index] = newValue;
+    return previousValue;
+  }
+
+  public void indexInsert(int index, int key, long value) {
+    assert index < 0 : "The index must not point at an existing key.";
+
+    index = ~index;
+    if (((key) == 0)) {
+      assert index == mask + 1;
+      values[index] = value;
+      hasEmptyKey = true;
+    } else {
+      assert ((keys[index]) == 0);
+
+      if (assigned == resizeAt) {
+        allocateThenInsertThenRehash(index, key, value);
+      } else {
+        keys[index] = key;
+        values[index] = value;
+      }
+
+      assigned++;
+    }
+  }
+
+  public long indexRemove(int index) {
+    assert index >= 0 : "The index must point at an existing key.";
+    assert index <= mask || (index == mask + 1 && hasEmptyKey);
+
+    long previousValue = values[index];
+    if (index > mask) {
+      assert index == mask + 1;
+      hasEmptyKey = false;
+      values[index] = 0L;
+    } else {
+      shiftConflictingKeys(index);
+    }
+    return previousValue;
+  }
+
+  public void clear() {
+    assigned = 0;
+    hasEmptyKey = false;
+
+    Arrays.fill(keys, 0);
+  }
+
+  public void release() {
+    assigned = 0;
+    hasEmptyKey = false;
+
+    keys = null;
+    values = null;
+    ensureCapacity(DEFAULT_EXPECTED_ELEMENTS);
+  }
+
+  public int size() {
+    return assigned + (hasEmptyKey ? 1 : 0);
+  }
+
+  public boolean isEmpty() {
+    return size() == 0;
+  }
+
+  @Override
+  public int hashCode() {
+    int h = hasEmptyKey ? 0xDEADBEEF : 0;
+    for (IntLongCursor c : this) {
+      h += BitMixer.mix(c.key) + BitMixer.mix(c.value);
+    }
+    return h;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    return (this == obj)
+        || (obj != null && getClass() == obj.getClass() && equalElements(getClass().cast(obj)));
+  }
+
+  /** Return true if all keys of some other container exist in this container. */
+  protected boolean equalElements(IntLongHashMap other) {
+    if (other.size() != size()) {
+      return false;
+    }
+
+    for (IntLongCursor c : other) {
+      int key = c.key;
+      if (!containsKey(key) || !((c.value) == (get(key)))) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  /**
+   * Ensure this container can hold at least the given number of keys (entries) without resizing its
+   * buffers.
+   *
+   * @param expectedElements The total number of keys, inclusive.
+   */
+  public void ensureCapacity(int expectedElements) {
+    if (expectedElements > resizeAt || keys == null) {
+      final int[] prevKeys = this.keys;
+      final long[] prevValues = this.values;
+      allocateBuffers(minBufferSize(expectedElements, loadFactor));
+      if (prevKeys != null && !isEmpty()) {
+        rehash(prevKeys, prevValues);
+      }
+    }
+  }
+
+  @Override
+  public long ramBytesUsed() {
+    return BASE_RAM_BYTES_USED + RamUsageEstimator.sizeOf(keys) + RamUsageEstimator.sizeOf(values);
+  }
+
+  /**
+   * Provides the next iteration seed used to build the iteration starting slot and offset
+   * increment. This method does not need to be synchronized, what matters is that each thread gets
+   * a sequence of varying seeds.
+   */
+  protected int nextIterationSeed() {
+    return iterationSeed = BitMixer.mixPhi(iterationSeed);
+  }
+
+  /** An iterator implementation for {@link #iterator}. */
+  private final class EntryIterator extends AbstractIterator<IntLongCursor> {
+    private final IntLongCursor cursor;
+    private final int increment;
+    private int index;
+    private int slot;
+
+    public EntryIterator() {
+      cursor = new IntLongCursor();
+      int seed = nextIterationSeed();
+      increment = iterationIncrement(seed);
+      slot = seed & mask;
+    }
+
+    @Override
+    protected IntLongCursor fetch() {
+      final int mask = IntLongHashMap.this.mask;
+      while (index <= mask) {
+        int existing;
+        index++;
+        slot = (slot + increment) & mask;
+        if (!((existing = keys[slot]) == 0)) {
+          cursor.index = slot;
+          cursor.key = existing;
+          cursor.value = values[slot];
+          return cursor;
+        }
+      }
+
+      if (index == mask + 1 && hasEmptyKey) {
+        cursor.index = index;
+        cursor.key = 0;
+        cursor.value = values[index++];
+        return cursor;
+      }
+
+      return done();
+    }
+  }
+
+  @Override
+  public Iterator<IntLongCursor> iterator() {
+    return new EntryIterator();
+  }
+
+  /** Returns a specialized view of the keys of this associated container. */
+  public KeysContainer keys() {
+    return new KeysContainer();
+  }
+
+  /** A view of the keys inside this hash map. */
+  public final class KeysContainer implements Iterable<IntCursor> {
+    @Override
+    public Iterator<IntCursor> iterator() {
+      return new KeysIterator();
+    }
+
+    public int size() {
+      return IntLongHashMap.this.size();
+    }
+
+    public int[] toArray() {
+      int[] array = new int[size()];
+      int i = 0;
+      for (IntCursor cursor : this) {
+        array[i++] = cursor.value;
+      }
+      return array;
+    }
+  }
+
+  /** An iterator over the set of assigned keys. */
+  private final class KeysIterator extends AbstractIterator<IntCursor> {
+    private final IntCursor cursor;
+    private final int increment;
+    private int index;
+    private int slot;
+
+    public KeysIterator() {
+      cursor = new IntCursor();
+      int seed = nextIterationSeed();
+      increment = iterationIncrement(seed);
+      slot = seed & mask;
+    }
+
+    @Override
+    protected IntCursor fetch() {
+      final int mask = IntLongHashMap.this.mask;
+      while (index <= mask) {
+        int existing;
+        index++;
+        slot = (slot + increment) & mask;
+        if (!((existing = keys[slot]) == 0)) {
+          cursor.index = slot;
+          cursor.value = existing;
+          return cursor;
+        }
+      }
+
+      if (index == mask + 1 && hasEmptyKey) {
+        cursor.index = index++;
+        cursor.value = 0;
+        return cursor;
+      }
+
+      return done();
+    }
+  }
+
+  /**
+   * @return Returns a container with all values stored in this map.
+   */
+  public ValuesContainer values() {
+    return new ValuesContainer();
+  }
+
+  /** A view over the set of values of this map. */
+  public final class ValuesContainer implements Iterable<LongCursor> {
+    @Override
+    public Iterator<LongCursor> iterator() {
+      return new ValuesIterator();
+    }
+
+    public long[] toArray() {
+      long[] array = new long[size()];
+      int i = 0;
+      for (LongCursor cursor : this) {
+        array[i++] = cursor.value;
+      }
+      return array;
+    }
+  }
+
+  /** An iterator over the set of assigned values. */
+  private final class ValuesIterator extends AbstractIterator<LongCursor> {
+    private final LongCursor cursor;
+    private final int increment;
+    private int index;
+    private int slot;
+
+    public ValuesIterator() {
+      cursor = new LongCursor();
+      int seed = nextIterationSeed();
+      increment = iterationIncrement(seed);
+      slot = seed & mask;
+    }
+
+    @Override
+    protected LongCursor fetch() {
+      final int mask = IntLongHashMap.this.mask;
+      while (index <= mask) {
+        index++;
+        slot = (slot + increment) & mask;
+        if (!((keys[slot]) == 0)) {
+          cursor.index = slot;
+          cursor.value = values[slot];
+          return cursor;
+        }
+      }
+
+      if (index == mask + 1 && hasEmptyKey) {
+        cursor.index = index;
+        cursor.value = values[index++];
+        return cursor;
+      }
+
+      return done();
+    }
+  }
+
+  @Override
+  public IntLongHashMap clone() {
+    try {
+
+      IntLongHashMap cloned = (IntLongHashMap) super.clone();
+      cloned.keys = keys.clone();
+      cloned.values = values.clone();
+      cloned.hasEmptyKey = hasEmptyKey;
+      cloned.iterationSeed = ITERATION_SEED.incrementAndGet();
+      return cloned;
+    } catch (CloneNotSupportedException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  /** Convert the contents of this map to a human-friendly string. */
+  @Override
+  public String toString() {
+    final StringBuilder buffer = new StringBuilder();
+    buffer.append("[");
+
+    boolean first = true;
+    for (IntLongCursor cursor : this) {
+      if (!first) {
+        buffer.append(", ");
+      }
+      buffer.append(cursor.key);
+      buffer.append("=>");
+      buffer.append(cursor.value);
+      first = false;
+    }
+    buffer.append("]");
+    return buffer.toString();
+  }
+
+  /** Creates a hash map from two index-aligned arrays of key-value pairs. */
+  public static IntLongHashMap from(int[] keys, long[] values) {
+    if (keys.length != values.length) {
+      throw new IllegalArgumentException(
+          "Arrays of keys and values must have an identical length.");
+    }
+
+    IntLongHashMap map = new IntLongHashMap(keys.length);
+    for (int i = 0; i < keys.length; i++) {
+      map.put(keys[i], values[i]);
+    }
+
+    return map;
+  }
+
+  /**
+   * Returns a hash code for the given key.
+   *
+   * <p>The output from this function should evenly distribute keys across the entire integer range.
+   */
+  protected int hashKey(int key) {
+    assert !((key) == 0); // Handled as a special case (empty slot marker).
+    return BitMixer.mixPhi(key);
+  }
+
+  /**
+   * Validate load factor range and return it. Override and suppress if you need insane load
+   * factors.
+   */
+  protected double verifyLoadFactor(double loadFactor) {
+    checkLoadFactor(loadFactor, MIN_LOAD_FACTOR, MAX_LOAD_FACTOR);
+    return loadFactor;
+  }
+
+  /** Rehash from old buffers to new buffers. */
+  protected void rehash(int[] fromKeys, long[] fromValues) {
+    assert fromKeys.length == fromValues.length
+        && HashContainers.checkPowerOfTwo(fromKeys.length - 1);
+
+    // Rehash all stored key/value pairs into the new buffers.
+    final int[] keys = this.keys;
+    final long[] values = this.values;
+    final int mask = this.mask;
+    int existing;
+
+    // Copy the zero element's slot, then rehash everything else.
+    int from = fromKeys.length - 1;
+    keys[keys.length - 1] = fromKeys[from];
+    values[values.length - 1] = fromValues[from];
+    while (--from >= 0) {
+      if (!((existing = fromKeys[from]) == 0)) {
+        int slot = hashKey(existing) & mask;
+        while (!((keys[slot]) == 0)) {
+          slot = (slot + 1) & mask;
+        }
+        keys[slot] = existing;
+        values[slot] = fromValues[from];
+      }
+    }
+  }
+
+  /**
+   * Allocate new internal buffers. This method attempts to allocate and assign internal buffers
+   * atomically (either allocations succeed or not).
+   */
+  protected void allocateBuffers(int arraySize) {
+    assert Integer.bitCount(arraySize) == 1;
+
+    // Ensure no change is done if we hit an OOM.
+    int[] prevKeys = this.keys;
+    long[] prevValues = this.values;
+    try {
+      int emptyElementSlot = 1;
+      this.keys = (new int[arraySize + emptyElementSlot]);
+      this.values = (new long[arraySize + emptyElementSlot]);
+    } catch (OutOfMemoryError e) {
+      this.keys = prevKeys;
+      this.values = prevValues;
+      throw new BufferAllocationException(
+          "Not enough memory to allocate buffers for rehashing: %,d -> %,d",
+          e, this.mask + 1, arraySize);
+    }
+
+    this.resizeAt = expandAtCount(arraySize, loadFactor);
+    this.mask = arraySize - 1;
+  }
+
+  /**
+   * This method is invoked when there is a new key/ value pair to be inserted into the buffers but
+   * there is not enough empty slots to do so.
+   *
+   * <p>New buffers are allocated. If this succeeds, we know we can proceed with rehashing so we
+   * assign the pending element to the previous buffer (possibly violating the invariant of having
+   * at least one empty slot) and rehash all keys, substituting new buffers at the end.
+   */
+  protected void allocateThenInsertThenRehash(int slot, int pendingKey, long pendingValue) {
+    assert assigned == resizeAt && ((keys[slot]) == 0) && !((pendingKey) == 0);
+
+    // Try to allocate new buffers first. If we OOM, we leave in a consistent state.
+    final int[] prevKeys = this.keys;
+    final long[] prevValues = this.values;
+    allocateBuffers(nextBufferSize(mask + 1, size(), loadFactor));
+    assert this.keys.length > prevKeys.length;
+
+    // We have succeeded at allocating new data so insert the pending key/value at
+    // the free slot in the old arrays before rehashing.
+    prevKeys[slot] = pendingKey;
+    prevValues[slot] = pendingValue;
+
+    // Rehash old keys, including the pending key.
+    rehash(prevKeys, prevValues);
+  }
+
+  /**
+   * Shift all the slot-conflicting keys and values allocated to (and including) <code>slot</code>.
+   */
+  protected void shiftConflictingKeys(int gapSlot) {
+    final int[] keys = this.keys;
+    final long[] values = this.values;
+    final int mask = this.mask;
+
+    // Perform shifts of conflicting keys to fill in the gap.
+    int distance = 0;
+    while (true) {
+      final int slot = (gapSlot + (++distance)) & mask;
+      final int existing = keys[slot];
+      if (((existing) == 0)) {
+        break;
+      }
+
+      final int idealSlot = hashKey(existing);
+      final int shift = (slot - idealSlot) & mask;
+      if (shift >= distance) {
+        // Entry at this position was originally at or before the gap slot.
+        // Move the conflict-shifted entry to the gap's position and repeat the procedure
+        // for any entries to the right of the current position, treating it
+        // as the new gap.
+        keys[gapSlot] = existing;
+        values[gapSlot] = values[slot];
+        gapSlot = slot;
+        distance = 0;
+      }
+    }
+
+    // Mark the last found gap slot without a conflict as empty.
+    keys[gapSlot] = 0;
+    values[gapSlot] = 0L;
+    assigned--;
+  }
+
+  /** Forked from HPPC, holding int index,key and value */
+  public static final class IntLongCursor {
+    /**
+     * The current key and value's index in the container this cursor belongs to. The meaning of
+     * this index is defined by the container (usually it will be an index in the underlying storage
+     * buffer).
+     */
+    public int index;
+
+    /** The current key. */
+    public int key;
+
+    /** The current value. */
+    public long value;
+
+    @Override
+    public String toString() {
+      return "[cursor, index: " + index + ", key: " + key + ", value: " + value + "]";
+    }
+  }
+}

lucene/core/src/java/org/apache/lucene/internal/vectorization/DefaultPostingDecodingUtil.java

@@ -0,0 +1,42 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.internal.vectorization;
+
+import java.io.IOException;
+import org.apache.lucene.store.IndexInput;
+
+final class DefaultPostingDecodingUtil extends PostingDecodingUtil {
+
+  protected final IndexInput in;
+
+  public DefaultPostingDecodingUtil(IndexInput in) {
+    this.in = in;
+  }
+
+  @Override
+  public void splitLongs(
+      int count, long[] b, int bShift, long bMask, long[] c, int cIndex, long cMask)
+      throws IOException {
+    assert count <= 64;
+    in.readLongs(c, cIndex, count);
+    // The below loop is auto-vectorized
+    for (int i = 0; i < count; ++i) {
+      b[i] = (c[cIndex + i] >>> bShift) & bMask;
+      c[cIndex + i] &= cMask;
+    }
+  }
+}

lucene/core/src/java/org/apache/lucene/internal/vectorization/DefaultVectorizationProvider.java

@@ -20,6 +20,7 @@ package org.apache.lucene.internal.vectorization;
 import org.apache.lucene.codecs.hnsw.DefaultFlatVectorScorer;
 import org.apache.lucene.codecs.hnsw.FlatVectorsScorer;
 import org.apache.lucene.codecs.lucene99.Lucene99ScalarQuantizedVectorScorer;
+import org.apache.lucene.store.IndexInput;
 
 /** Default provider returning scalar implementations. */
 final class DefaultVectorizationProvider extends VectorizationProvider {
@@ -44,4 +45,9 @@ final class DefaultVectorizationProvider extends VectorizationProvider {
   public FlatVectorsScorer getLucene99ScalarQuantizedVectorsScorer() {
     return new Lucene99ScalarQuantizedVectorScorer(getLucene99FlatVectorsScorer());
   }
+
+  @Override
+  public PostingDecodingUtil newPostingDecodingUtil(IndexInput input) {
+    return new DefaultPostingDecodingUtil(input);
+  }
 }

lucene/core/src/java/org/apache/lucene/internal/vectorization/PostingDecodingUtil.java

@@ -0,0 +1,32 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.internal.vectorization;
+
+import java.io.IOException;
+
+/** Utility class to decode postings. */
+public abstract class PostingDecodingUtil {
+
+  /**
+   * Read {@code count} longs. This number must not exceed 64. Apply shift {@code bShift} and mask
+   * {@code bMask} and store the result in {@code b} starting at offset 0. Apply mask {@code cMask}
+   * and store the result in {@code c} starting at offset {@code cIndex}.
+   */
+  public abstract void splitLongs(
+      int count, long[] b, int bShift, long bMask, long[] c, int cIndex, long cMask)
+      throws IOException;
+}

lucene/core/src/java/org/apache/lucene/internal/vectorization/VectorizationProvider.java

@@ -17,6 +17,7 @@
 
 package org.apache.lucene.internal.vectorization;
 
+import java.io.IOException;
 import java.lang.StackWalker.StackFrame;
 import java.lang.invoke.MethodHandles;
 import java.lang.invoke.MethodType;
@@ -28,6 +29,7 @@ import java.util.function.Predicate;
 import java.util.logging.Logger;
 import java.util.stream.Stream;
 import org.apache.lucene.codecs.hnsw.FlatVectorsScorer;
+import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.util.Constants;
 import org.apache.lucene.util.VectorUtil;
 
@@ -98,6 +100,9 @@ public abstract class VectorizationProvider {
   /** Returns a FlatVectorsScorer that supports scalar quantized vectors in the Lucene99 format. */
   public abstract FlatVectorsScorer getLucene99ScalarQuantizedVectorsScorer();
 
+  /** Create a new {@link PostingDecodingUtil} for the given {@link IndexInput}. */
+  public abstract PostingDecodingUtil newPostingDecodingUtil(IndexInput input) throws IOException;
+
   // *** Lookup mechanism: ***
 
   private static final Logger LOG = Logger.getLogger(VectorizationProvider.class.getName());
@@ -187,7 +192,8 @@ public abstract class VectorizationProvider {
   private static final Set<String> VALID_CALLERS =
       Set.of(
           "org.apache.lucene.codecs.hnsw.FlatVectorScorerUtil",
-          "org.apache.lucene.util.VectorUtil");
+          "org.apache.lucene.util.VectorUtil",
+          "org.apache.lucene.codecs.lucene912.PostingIndexInput");
 
   private static void ensureCaller() {
     final boolean validCaller =

lucene/core/src/java/org/apache/lucene/search/AbstractMultiTermQueryConstantScoreWrapper.java

@@ -154,38 +154,17 @@ abstract class AbstractMultiTermQueryConstantScoreWrapper<Q extends MultiTermQue
         List<TermAndState> collectedTerms)
         throws IOException;
 
-    private IOSupplier<WeightOrDocIdSetIterator> rewrite(LeafReaderContext context, Terms terms)
-        throws IOException {
-      assert terms != null;
-
-      final int fieldDocCount = terms.getDocCount();
-      final TermsEnum termsEnum = q.getTermsEnum(terms);
-      assert termsEnum != null;
-
-      final List<TermAndState> collectedTerms = new ArrayList<>();
-      boolean collectResult = collectTerms(fieldDocCount, termsEnum, collectedTerms);
-      if (collectResult && collectedTerms.isEmpty()) {
-        return null;
+    private WeightOrDocIdSetIterator rewriteAsBooleanQuery(
+        LeafReaderContext context, List<TermAndState> collectedTerms) throws IOException {
+      BooleanQuery.Builder bq = new BooleanQuery.Builder();
+      for (TermAndState t : collectedTerms) {
+        final TermStates termStates = new TermStates(searcher.getTopReaderContext());
+        termStates.register(t.state, context.ord, t.docFreq, t.totalTermFreq);
+        bq.add(new TermQuery(new Term(q.field, t.term), termStates), BooleanClause.Occur.SHOULD);
       }
-      return () -> {
-        if (collectResult) {
-          // build a boolean query
-          BooleanQuery.Builder bq = new BooleanQuery.Builder();
-          for (TermAndState t : collectedTerms) {
-            final TermStates termStates = new TermStates(searcher.getTopReaderContext());
-            termStates.register(t.state, context.ord, t.docFreq, t.totalTermFreq);
-            bq.add(
-                new TermQuery(new Term(q.field, t.term), termStates), BooleanClause.Occur.SHOULD);
-          }
-          Query q = new ConstantScoreQuery(bq.build());
-          final Weight weight = searcher.rewrite(q).createWeight(searcher, scoreMode, score());
-          return new WeightOrDocIdSetIterator(weight);
-        } else {
-          // Too many terms to rewrite as a simple bq.
-          // Invoke rewriteInner logic to handle rewriting:
-          return rewriteInner(context, fieldDocCount, terms, termsEnum, collectedTerms);
-        }
-      };
+      Query q = new ConstantScoreQuery(bq.build());
+      final Weight weight = searcher.rewrite(q).createWeight(searcher, scoreMode, score());
+      return new WeightOrDocIdSetIterator(weight);
     }
 
     private boolean collectTerms(int fieldDocCount, TermsEnum termsEnum, List<TermAndState> terms)
@@ -240,9 +219,44 @@ abstract class AbstractMultiTermQueryConstantScoreWrapper<Q extends MultiTermQue
         return null;
       }
 
-      final long cost = estimateCost(terms, q.getTermsCount());
-      IOSupplier<WeightOrDocIdSetIterator> weightOrIteratorSupplier = rewrite(context, terms);
-      if (weightOrIteratorSupplier == null) return null;
+      assert terms != null;
+
+      final int fieldDocCount = terms.getDocCount();
+      final TermsEnum termsEnum = q.getTermsEnum(terms);
+      assert termsEnum != null;
+
+      List<TermAndState> collectedTerms = new ArrayList<>();
+      boolean collectResult = collectTerms(fieldDocCount, termsEnum, collectedTerms);
+
+      final long cost;
+      if (collectResult) {
+        // Return a null supplier if no query terms were in the segment:
+        if (collectedTerms.isEmpty()) {
+          return null;
+        }
+
+        // TODO: Instead of replicating the cost logic of a BooleanQuery we could consider rewriting
+        // to a BQ eagerly at this point and delegating to its cost method (instead of lazily
+        // rewriting on #get). Not sure what the performance hit would be of doing this though.
+        long sumTermCost = 0;
+        for (TermAndState collectedTerm : collectedTerms) {
+          sumTermCost += collectedTerm.docFreq;
+        }
+        cost = sumTermCost;
+      } else {
+        cost = estimateCost(terms, q.getTermsCount());
+      }
+
+      IOSupplier<WeightOrDocIdSetIterator> weightOrIteratorSupplier =
+          () -> {
+            if (collectResult) {
+              return rewriteAsBooleanQuery(context, collectedTerms);
+            } else {
+              // Too many terms to rewrite as a simple bq.
+              // Invoke rewriteInner logic to handle rewriting:
+              return rewriteInner(context, fieldDocCount, terms, termsEnum, collectedTerms);
+            }
+          };
 
       return new ScorerSupplier() {
         @Override

lucene/core/src/java/org/apache/lucene/search/AbstractVectorSimilarityQuery.java

@@ -23,6 +23,8 @@ import java.util.List;
 import java.util.Objects;
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.QueryTimeout;
+import org.apache.lucene.search.knn.KnnCollectorManager;
 import org.apache.lucene.util.BitSet;
 import org.apache.lucene.util.BitSetIterator;
 import org.apache.lucene.util.Bits;
@@ -58,10 +60,19 @@ abstract class AbstractVectorSimilarityQuery extends Query {
     this.filter = filter;
   }
 
+  protected KnnCollectorManager getKnnCollectorManager() {
+    return (visitedLimit, context) ->
+        new VectorSimilarityCollector(traversalSimilarity, resultSimilarity, visitedLimit);
+  }
+
   abstract VectorScorer createVectorScorer(LeafReaderContext context) throws IOException;
 
   protected abstract TopDocs approximateSearch(
-      LeafReaderContext context, Bits acceptDocs, int visitLimit) throws IOException;
+      LeafReaderContext context,
+      Bits acceptDocs,
+      int visitLimit,
+      KnnCollectorManager knnCollectorManager)
+      throws IOException;
 
   @Override
   public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)
@@ -72,6 +83,10 @@ abstract class AbstractVectorSimilarityQuery extends Query {
               ? null
               : searcher.createWeight(searcher.rewrite(filter), ScoreMode.COMPLETE_NO_SCORES, 1);
 
+      final QueryTimeout queryTimeout = searcher.getTimeout();
+      final TimeLimitingKnnCollectorManager timeLimitingKnnCollectorManager =
+          new TimeLimitingKnnCollectorManager(getKnnCollectorManager(), queryTimeout);
+
       @Override
       public Explanation explain(LeafReaderContext context, int doc) throws IOException {
         if (filterWeight != null) {
@@ -103,16 +118,14 @@ abstract class AbstractVectorSimilarityQuery extends Query {
       public ScorerSupplier scorerSupplier(LeafReaderContext context) throws IOException {
         LeafReader leafReader = context.reader();
         Bits liveDocs = leafReader.getLiveDocs();
-        final Scorer vectorSimilarityScorer;
+
         // If there is no filter
         if (filterWeight == null) {
           // Return exhaustive results
-          TopDocs results = approximateSearch(context, liveDocs, Integer.MAX_VALUE);
-          if (results.scoreDocs.length == 0) {
-            return null;
-          }
-          vectorSimilarityScorer =
-              VectorSimilarityScorer.fromScoreDocs(this, boost, results.scoreDocs);
+          TopDocs results =
+              approximateSearch(
+                  context, liveDocs, Integer.MAX_VALUE, timeLimitingKnnCollectorManager);
+          return VectorSimilarityScorerSupplier.fromScoreDocs(boost, results.scoreDocs);
         } else {
           Scorer scorer = filterWeight.scorer(context);
           if (scorer == null) {
@@ -143,27 +156,23 @@ abstract class AbstractVectorSimilarityQuery extends Query {
           }
 
           // Perform an approximate search
-          TopDocs results = approximateSearch(context, acceptDocs, cardinality);
+          TopDocs results =
+              approximateSearch(context, acceptDocs, cardinality, timeLimitingKnnCollectorManager);
 
-          // If the limit was exhausted
-          if (results.totalHits.relation == TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO) {
-            // Return a lazy-loading iterator
-            vectorSimilarityScorer =
-                VectorSimilarityScorer.fromAcceptDocs(
-                    this,
-                    boost,
-                    createVectorScorer(context),
-                    new BitSetIterator(acceptDocs, cardinality),
-                    resultSimilarity);
-          } else if (results.scoreDocs.length == 0) {
-            return null;
-          } else {
+          if (results.totalHits.relation == TotalHits.Relation.EQUAL_TO
+              // Return partial results only when timeout is met
+              || (queryTimeout != null && queryTimeout.shouldExit())) {
             // Return an iterator over the collected results
-            vectorSimilarityScorer =
-                VectorSimilarityScorer.fromScoreDocs(this, boost, results.scoreDocs);
+            return VectorSimilarityScorerSupplier.fromScoreDocs(boost, results.scoreDocs);
+          } else {
+            // Return a lazy-loading iterator
+            return VectorSimilarityScorerSupplier.fromAcceptDocs(
+                boost,
+                createVectorScorer(context),
+                new BitSetIterator(acceptDocs, cardinality),
+                resultSimilarity);
           }
         }
-        return new DefaultScorerSupplier(vectorSimilarityScorer);
       }
 
       @Override
@@ -197,16 +206,20 @@ abstract class AbstractVectorSimilarityQuery extends Query {
     return Objects.hash(field, traversalSimilarity, resultSimilarity, filter);
   }
 
-  private static class VectorSimilarityScorer extends Scorer {
+  private static class VectorSimilarityScorerSupplier extends ScorerSupplier {
     final DocIdSetIterator iterator;
     final float[] cachedScore;
 
-    VectorSimilarityScorer(DocIdSetIterator iterator, float[] cachedScore) {
+    VectorSimilarityScorerSupplier(DocIdSetIterator iterator, float[] cachedScore) {
       this.iterator = iterator;
       this.cachedScore = cachedScore;
     }
 
-    static VectorSimilarityScorer fromScoreDocs(Weight weight, float boost, ScoreDoc[] scoreDocs) {
+    static VectorSimilarityScorerSupplier fromScoreDocs(float boost, ScoreDoc[] scoreDocs) {
+      if (scoreDocs.length == 0) {
+        return null;
+      }
+
       // Sort in ascending order of docid
       Arrays.sort(scoreDocs, Comparator.comparingInt(scoreDoc -> scoreDoc.doc));
 
@@ -252,18 +265,15 @@ abstract class AbstractVectorSimilarityQuery extends Query {
             }
           };
 
-      return new VectorSimilarityScorer(iterator, cachedScore);
+      return new VectorSimilarityScorerSupplier(iterator, cachedScore);
     }
 
-    static VectorSimilarityScorer fromAcceptDocs(
-        Weight weight,
-        float boost,
-        VectorScorer scorer,
-        DocIdSetIterator acceptDocs,
-        float threshold) {
+    static VectorSimilarityScorerSupplier fromAcceptDocs(
+        float boost, VectorScorer scorer, DocIdSetIterator acceptDocs, float threshold) {
       if (scorer == null) {
         return null;
       }
+
       float[] cachedScore = new float[1];
       DocIdSetIterator vectorIterator = scorer.iterator();
       DocIdSetIterator conjunction =
@@ -281,27 +291,37 @@ abstract class AbstractVectorSimilarityQuery extends Query {
             }
           };
 
-      return new VectorSimilarityScorer(iterator, cachedScore);
+      return new VectorSimilarityScorerSupplier(iterator, cachedScore);
     }
 
     @Override
-    public int docID() {
-      return iterator.docID();
+    public Scorer get(long leadCost) {
+      return new Scorer() {
+        @Override
+        public int docID() {
+          return iterator.docID();
+        }
+
+        @Override
+        public DocIdSetIterator iterator() {
+          return iterator;
+        }
+
+        @Override
+        public float getMaxScore(int upTo) {
+          return Float.POSITIVE_INFINITY;
+        }
+
+        @Override
+        public float score() {
+          return cachedScore[0];
+        }
+      };
     }
 
     @Override
-    public DocIdSetIterator iterator() {
-      return iterator;
-    }
-
-    @Override
-    public float getMaxScore(int upTo) {
-      return Float.POSITIVE_INFINITY;
-    }
-
-    @Override
-    public float score() {
-      return cachedScore[0];
+    public long cost() {
+      return iterator.cost();
     }
   }
 }

lucene/core/src/java/org/apache/lucene/search/BooleanScorer.java

@@ -30,7 +30,7 @@ import org.apache.lucene.util.PriorityQueue;
  */
 final class BooleanScorer extends BulkScorer {
 
-  static final int SHIFT = 11;
+  static final int SHIFT = 12;
   static final int SIZE = 1 << SHIFT;
   static final int MASK = SIZE - 1;
   static final int SET_SIZE = 1 << (SHIFT - 6);

lucene/core/src/java/org/apache/lucene/search/ByteVectorSimilarityQuery.java

@@ -23,6 +23,7 @@ import java.util.Objects;
 import org.apache.lucene.document.KnnByteVectorField;
 import org.apache.lucene.index.ByteVectorValues;
 import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.search.knn.KnnCollectorManager;
 import org.apache.lucene.util.Bits;
 
 /**
@@ -106,10 +107,13 @@ public class ByteVectorSimilarityQuery extends AbstractVectorSimilarityQuery {
 
   @Override
   @SuppressWarnings("resource")
-  protected TopDocs approximateSearch(LeafReaderContext context, Bits acceptDocs, int visitLimit)
+  protected TopDocs approximateSearch(
+      LeafReaderContext context,
+      Bits acceptDocs,
+      int visitLimit,
+      KnnCollectorManager knnCollectorManager)
       throws IOException {
-    KnnCollector collector =
-        new VectorSimilarityCollector(traversalSimilarity, resultSimilarity, visitLimit);
+    KnnCollector collector = knnCollectorManager.newCollector(visitLimit, context);
     context.reader().searchNearestVectors(field, target, collector, acceptDocs);
     return collector.topDocs();
   }

lucene/core/src/java/org/apache/lucene/search/CollectorOwner.java

@@ -0,0 +1,78 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.search;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * This class wraps {@link CollectorManager} and owns the collectors the manager creates. It is
+ * convenient that clients of the class don't have to worry about keeping the list of collectors, as
+ * well as about making the collector's type (C) compatible when reduce is called. Instances of this
+ * class cache results of {@link CollectorManager#reduce(Collection)}.
+ *
+ * <p>Note that instance of this class ignores any {@link Collector} created by {@link
+ * CollectorManager#newCollector()} directly, not through {@link #newCollector()}
+ *
+ * @lucene.experimental
+ */
+public final class CollectorOwner<C extends Collector, T> {
+
+  private final CollectorManager<C, T> manager;
+
+  private T result;
+  private boolean reduced;
+
+  // TODO: For IndexSearcher, the list doesn't have to be synchronized
+  //  because we create new collectors sequentially. Drill sideways creates new collectors in
+  //  DrillSidewaysQuery#Weight#bulkScorer which is already called concurrently.
+  //  I think making the list synchronized here is not a huge concern, at the same time, do we want
+  //  to do something about it?
+  //  e.g. have boolean property in constructor that makes it threads friendly when set?
+  private final List<C> collectors = Collections.synchronizedList(new ArrayList<>());
+
+  public CollectorOwner(CollectorManager<C, T> manager) {
+    this.manager = manager;
+  }
+
+  /** Return a new {@link Collector}. This must return a different instance on each call. */
+  public C newCollector() throws IOException {
+    C collector = manager.newCollector();
+    collectors.add(collector);
+    return collector;
+  }
+
+  public C getCollector(int i) {
+    return collectors.get(i);
+  }
+
+  /**
+   * Returns result of {@link CollectorManager#reduce(Collection)}. The result is cached.
+   *
+   * <p>This method is NOT threadsafe.
+   */
+  public T getResult() throws IOException {
+    if (reduced == false) {
+      result = manager.reduce(collectors);
+      reduced = true;
+    }
+    return result;
+  }
+}

lucene/core/src/java/org/apache/lucene/search/DoubleValuesSource.java

@@ -26,6 +26,7 @@ import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.index.VectorEncoding;
 import org.apache.lucene.search.comparators.DoubleComparator;
+import org.apache.lucene.util.NumericUtils;
 
 /**
  * Base class for producing {@link DoubleValues}
@@ -115,6 +116,70 @@ public abstract class DoubleValuesSource implements SegmentCacheable {
     return new LongDoubleValuesSource(this);
   }
 
+  /** Convert to {@link LongValuesSource} by calling {@link NumericUtils#doubleToSortableLong} */
+  public final LongValuesSource toSortableLongDoubleValuesSource() {
+    return new SortableLongDoubleValuesSource(this);
+  }
+
+  private static class SortableLongDoubleValuesSource extends LongValuesSource {
+
+    private final DoubleValuesSource inner;
+
+    private SortableLongDoubleValuesSource(DoubleValuesSource inner) {
+      this.inner = Objects.requireNonNull(inner);
+    }
+
+    @Override
+    public LongValues getValues(LeafReaderContext ctx, DoubleValues scores) throws IOException {
+      DoubleValues in = inner.getValues(ctx, scores);
+
+      return new LongValues() {
+        @Override
+        public long longValue() throws IOException {
+          return NumericUtils.doubleToSortableLong(in.doubleValue());
+        }
+
+        @Override
+        public boolean advanceExact(int doc) throws IOException {
+          return in.advanceExact(doc);
+        }
+      };
+    }
+
+    @Override
+    public boolean needsScores() {
+      return inner.needsScores();
+    }
+
+    @Override
+    public int hashCode() {
+      return inner.hashCode();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      if (this == o) return true;
+      if (o == null || getClass() != o.getClass()) return false;
+      SortableLongDoubleValuesSource that = (SortableLongDoubleValuesSource) o;
+      return Objects.equals(inner, that.inner);
+    }
+
+    @Override
+    public String toString() {
+      return "sortableLong(" + inner.toString() + ")";
+    }
+
+    @Override
+    public LongValuesSource rewrite(IndexSearcher searcher) throws IOException {
+      return inner.rewrite(searcher).toLongValuesSource();
+    }
+
+    @Override
+    public boolean isCacheable(LeafReaderContext ctx) {
+      return false;
+    }
+  }
+
   private static class LongDoubleValuesSource extends LongValuesSource {
 
     private final DoubleValuesSource inner;

lucene/core/src/java/org/apache/lucene/search/FloatVectorSimilarityQuery.java

@@ -23,6 +23,7 @@ import java.util.Objects;
 import org.apache.lucene.document.KnnFloatVectorField;
 import org.apache.lucene.index.FloatVectorValues;
 import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.search.knn.KnnCollectorManager;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.VectorUtil;
 
@@ -108,10 +109,13 @@ public class FloatVectorSimilarityQuery extends AbstractVectorSimilarityQuery {
 
   @Override
   @SuppressWarnings("resource")
-  protected TopDocs approximateSearch(LeafReaderContext context, Bits acceptDocs, int visitLimit)
+  protected TopDocs approximateSearch(
+      LeafReaderContext context,
+      Bits acceptDocs,
+      int visitLimit,
+      KnnCollectorManager knnCollectorManager)
       throws IOException {
-    KnnCollector collector =
-        new VectorSimilarityCollector(traversalSimilarity, resultSimilarity, visitLimit);
+    KnnCollector collector = knnCollectorManager.newCollector(visitLimit, context);
     context.reader().searchNearestVectors(field, target, collector, acceptDocs);
     return collector.topDocs();
   }

lucene/core/src/java/org/apache/lucene/search/HitsThresholdChecker.java

@@ -24,6 +24,10 @@ abstract class HitsThresholdChecker {
   /** Implementation of HitsThresholdChecker which allows global hit counting */
   private static class GlobalHitsThresholdChecker extends HitsThresholdChecker {
     private final LongAdder globalHitCount = new LongAdder();
+    // Cache whether the threshold has been reached already. It is not volatile or synchronized on
+    // purpose to contain the overhead of reading the value similarly to what String#hashCode()
+    // does. This does not affect correctness.
+    private boolean thresholdReached = false;
 
     GlobalHitsThresholdChecker(int totalHitsThreshold) {
       super(totalHitsThreshold);
@@ -32,12 +36,17 @@ abstract class HitsThresholdChecker {
 
     @Override
     void incrementHitCount() {
-      globalHitCount.increment();
+      if (thresholdReached == false) {
+        globalHitCount.increment();
+      }
     }
 
     @Override
     boolean isThresholdReached() {
-      return globalHitCount.longValue() > getHitsThreshold();
+      if (thresholdReached) {
+        return true;
+      }
+      return thresholdReached = globalHitCount.longValue() > getHitsThreshold();
     }
 
     @Override

lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java

@@ -671,10 +671,58 @@ public class IndexSearcher {
     }
   }
 
+  /**
+   * Lower-level search API. Search all leaves using the given {@link CollectorOwner}, without
+   * calling {@link CollectorOwner#getResult()} so that clients can reduce and read results
+   * themselves.
+   *
+   * <p>Note that this method doesn't return anything - users can access results by calling {@link
+   * CollectorOwner#getResult()}
+   *
+   * @lucene.experimental
+   */
+  public <C extends Collector> void search(Query query, CollectorOwner<C, ?> collectorOwner)
+      throws IOException {
+    final C firstCollector = collectorOwner.newCollector();
+    query = rewrite(query, firstCollector.scoreMode().needsScores());
+    final Weight weight = createWeight(query, firstCollector.scoreMode(), 1);
+    search(weight, collectorOwner, firstCollector);
+  }
+
+  private <C extends Collector> void search(
+      Weight weight, CollectorOwner<C, ?> collectorOwner, C firstCollector) throws IOException {
+    final LeafSlice[] leafSlices = getSlices();
+    if (leafSlices.length == 0) {
+      // there are no segments, nothing to offload to the executor
+      assert leafContexts.isEmpty();
+    } else {
+      final ScoreMode scoreMode = firstCollector.scoreMode();
+      for (int i = 1; i < leafSlices.length; ++i) {
+        final C collector = collectorOwner.newCollector();
+        if (scoreMode != collector.scoreMode()) {
+          throw new IllegalStateException(
+              "CollectorManager does not always produce collectors with the same score mode");
+        }
+      }
+      final List<Callable<C>> listTasks = new ArrayList<>(leafSlices.length);
+      for (int i = 0; i < leafSlices.length; ++i) {
+        final LeafReaderContext[] leaves = leafSlices[i].leaves;
+        final C collector = collectorOwner.getCollector(i);
+        listTasks.add(
+            () -> {
+              search(Arrays.asList(leaves), weight, collector);
+              return collector;
+            });
+      }
+      taskExecutor.invokeAll(listTasks);
+    }
+  }
+
   /**
    * Lower-level search API.
    *
-   * <p>{@link LeafCollector#collect(int)} is called for every document. <br>
+   * <p>{@link #searchLeaf(LeafReaderContext, Weight, Collector)} is called for every leaf
+   * partition. <br>
    *
    * <p>NOTE: this method executes the searches on all given leaves exclusively. To search across
    * all the searchers leaves use {@link #leafContexts}.
@@ -694,40 +742,56 @@ public class IndexSearcher {
     // threaded...? the Collector could be sync'd?
     // always use single thread:
     for (LeafReaderContext ctx : leaves) { // search each subreader
-      final LeafCollector leafCollector;
+      searchLeaf(ctx, weight, collector);
+    }
+  }
+
+  /**
+   * Lower-level search API
+   *
+   * <p>{@link LeafCollector#collect(int)} is called for every document. <br>
+   *
+   * @param ctx the leaf to execute the search against
+   * @param weight to match document
+   * @param collector to receive hits
+   * @throws TooManyClauses If a query would exceed {@link IndexSearcher#getMaxClauseCount()}
+   *     clauses.
+   */
+  protected void searchLeaf(LeafReaderContext ctx, Weight weight, Collector collector)
+      throws IOException {
+    final LeafCollector leafCollector;
+    try {
+      leafCollector = collector.getLeafCollector(ctx);
+    } catch (
+        @SuppressWarnings("unused")
+        CollectionTerminatedException e) {
+      // there is no doc of interest in this reader context
+      // continue with the following leaf
+      return;
+    }
+    ScorerSupplier scorerSupplier = weight.scorerSupplier(ctx);
+    if (scorerSupplier != null) {
+      scorerSupplier.setTopLevelScoringClause();
+      BulkScorer scorer = scorerSupplier.bulkScorer();
+      if (queryTimeout != null) {
+        scorer = new TimeLimitingBulkScorer(scorer, queryTimeout);
+      }
       try {
-        leafCollector = collector.getLeafCollector(ctx);
+        scorer.score(leafCollector, ctx.reader().getLiveDocs());
       } catch (
           @SuppressWarnings("unused")
           CollectionTerminatedException e) {
-        // there is no doc of interest in this reader context
+        // collection was terminated prematurely
         // continue with the following leaf
-        continue;
+      } catch (
+          @SuppressWarnings("unused")
+          TimeLimitingBulkScorer.TimeExceededException e) {
+        partialResult = true;
       }
-      ScorerSupplier scorerSupplier = weight.scorerSupplier(ctx);
-      if (scorerSupplier != null) {
-        scorerSupplier.setTopLevelScoringClause();
-        BulkScorer scorer = scorerSupplier.bulkScorer();
-        if (queryTimeout != null) {
-          scorer = new TimeLimitingBulkScorer(scorer, queryTimeout);
-        }
-        try {
-          scorer.score(leafCollector, ctx.reader().getLiveDocs());
-        } catch (
-            @SuppressWarnings("unused")
-            CollectionTerminatedException e) {
-          // collection was terminated prematurely
-          // continue with the following leaf
-        } catch (
-            @SuppressWarnings("unused")
-            TimeLimitingBulkScorer.TimeExceededException e) {
-          partialResult = true;
-        }
-      }
-      // Note: this is called if collection ran successfully, including the above special cases of
-      // CollectionTerminatedException and TimeExceededException, but no other exception.
-      leafCollector.finish();
     }
+    // Note: this is called if collection ran successfully, including the above special cases of
+    // CollectionTerminatedException and TimeExceededException, but no other exception.
+    leafCollector.finish();
   }
 
   /**

lucene/core/src/java/org/apache/lucene/search/KnnByteVectorQuery.java

@@ -20,7 +20,7 @@ import java.io.IOException;
 import java.util.Arrays;
 import java.util.Objects;
 import org.apache.lucene.codecs.KnnVectorsReader;
-import org.apache.lucene.document.KnnFloatVectorField;
+import org.apache.lucene.document.KnnByteVectorField;
 import org.apache.lucene.index.ByteVectorValues;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.LeafReader;
@@ -52,7 +52,7 @@ public class KnnByteVectorQuery extends AbstractKnnVectorQuery {
    * Find the <code>k</code> nearest documents to the target vector according to the vectors in the
    * given field. <code>target</code> vector.
    *
-   * @param field a field that has been indexed as a {@link KnnFloatVectorField}.
+   * @param field a field that has been indexed as a {@link KnnByteVectorField}.
    * @param target the target of the search
    * @param k the number of documents to find
    * @throws IllegalArgumentException if <code>k</code> is less than 1
@@ -65,7 +65,7 @@ public class KnnByteVectorQuery extends AbstractKnnVectorQuery {
    * Find the <code>k</code> nearest documents to the target vector according to the vectors in the
    * given field. <code>target</code> vector.
    *
-   * @param field a field that has been indexed as a {@link KnnFloatVectorField}.
+   * @param field a field that has been indexed as a {@link KnnByteVectorField}.
    * @param target the target of the search
    * @param k the number of documents to find
    * @param filter a filter applied before the vector search

lucene/core/src/java/org/apache/lucene/search/MaxScoreBulkScorer.java

@@ -25,7 +25,7 @@ import org.apache.lucene.util.MathUtil;
 
 final class MaxScoreBulkScorer extends BulkScorer {
 
-  static final int INNER_WINDOW_SIZE = 1 << 11;
+  static final int INNER_WINDOW_SIZE = 1 << 12;
 
   private final int maxDoc;
   // All scorers, sorted by increasing max score.
@@ -271,11 +271,6 @@ final class MaxScoreBulkScorer extends BulkScorer {
       windowMax = (int) Math.min(windowMax, upTo + 1L); // upTo is inclusive
     }
 
-    // Score at least an entire inner window of docs
-    windowMax =
-        Math.max(
-            windowMax, (int) Math.min(Integer.MAX_VALUE, (long) windowMin + INNER_WINDOW_SIZE));
-
     return windowMax;
   }
 

lucene/core/src/java/org/apache/lucene/search/PhraseQuery.java

@@ -21,8 +21,8 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat;
-import org.apache.lucene.codecs.lucene99.Lucene99PostingsReader;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsFormat;
+import org.apache.lucene.codecs.lucene912.Lucene912PostingsReader;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
@@ -399,10 +399,10 @@ public class PhraseQuery extends Query {
   /**
    * A guess of the average number of simple operations for the initial seek and buffer refill per
    * document for the positions of a term. See also {@link
-   * Lucene99PostingsReader.BlockImpactsPostingsEnum#nextPosition()}.
+   * Lucene912PostingsReader.BlockImpactsPostingsEnum#nextPosition()}.
    *
    * <p>Aside: Instead of being constant this could depend among others on {@link
-   * Lucene99PostingsFormat#BLOCK_SIZE}, {@link TermsEnum#docFreq()}, {@link
+   * Lucene912PostingsFormat#BLOCK_SIZE}, {@link TermsEnum#docFreq()}, {@link
    * TermsEnum#totalTermFreq()}, {@link DocIdSetIterator#cost()} (expected number of matching docs),
    * {@link LeafReader#maxDoc()} (total number of docs in the segment), and the seek time and block
    * size of the device storing the index.
@@ -411,7 +411,7 @@ public class PhraseQuery extends Query {
 
   /**
    * Number of simple operations in {@link
-   * Lucene99PostingsReader.BlockImpactsPostingsEnum#nextPosition()} when no seek or buffer refill
+   * Lucene912PostingsReader.BlockImpactsPostingsEnum#nextPosition()} when no seek or buffer refill
    * is done.
    */
   private static final int TERM_OPS_PER_POS = 7;