Merge remote-tracking branch 'origin/master'

Conflicts:
	solr/CHANGES.txt

lucene/CHANGES.txt

@@ -65,6 +65,9 @@ New Features
   Polygon instances from a standard GeoJSON string (Robert Muir, Mike
   McCandless)
 
+* SOLR-9279: Queries module: new ComparisonBoolFunction base class
+  (Doug Turnbull via David Smiley)
+
 Bug Fixes
 
 * LUCENE-6662: Fixed potential resource leaks. (Rishabh Patel via Adrien Grand)
@@ -135,10 +138,9 @@ Improvements
 
 * LUCENE-7385: Improve/fix assert messages in SpanScorer. (David Smiley)
 
-* LUCENE-7390: Improve performance of indexing points by allowing the
-  codec to use transient heap in proportion to IndexWriter's RAM
-  buffer, instead of a fixed 16.0 MB.  A custom codec can still
-  override the buffer size itself. (Mike McCandless)
+* LUCENE-7393: Add ICUTokenizer option to parse Myanmar text as syllables instead of words,
+  because the ICU word-breaking algorithm has some issues. This allows for the previous 
+  tokenization used before Lucene 5. (AM, Robert Muir)
 
 Optimizations
 
@@ -154,6 +156,12 @@ Optimizations
 * LUCENE-7311: Cached term queries do not seek the terms dictionary anymore.
   (Adrien Grand)
 
+* LUCENE-7396, LUCENE-7399: Faster flush of points.
+  (Adrien Grand, Mike McCandless)
+
+* LUCENE-7406: Automaton and PrefixQuery tweaks (fewer object (re)allocations).
+  (Christine Poerschke)
+
 Other
 
 * LUCENE-4787: Fixed some highlighting javadocs. (Michael Dodsworth via Adrien

lucene/analysis/common/src/java/org/apache/lucene/analysis/minhash/MinHashFilter.java

@@ -402,6 +402,7 @@ public class MinHashFilter extends TokenFilter {
   }
 
   /** Returns the MurmurHash3_x64_128 hash, placing the result in "out". */
+  @SuppressWarnings("fallthrough") // the huge switch is designed to use fall through into cases!
   static void murmurhash3_x64_128(byte[] key, int offset, int len, int seed, LongPair out) {
     // The original algorithm does have a 32 bit unsigned seed.
     // We have to mask to match the behavior of the unsigned types and prevent sign extension.

lucene/analysis/icu/src/data/uax29/MyanmarSyllable.rbbi

@@ -0,0 +1,50 @@
+#
+# 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.
+#
+# 
+# Parses Myanmar text, with syllable as token. 
+#
+
+$Cons = [[:Other_Letter:]&[:Myanmar:]];
+$Virama = [\u1039];
+$Asat = [\u103A];
+
+$WordJoin = [:Line_Break=Word_Joiner:]; 
+
+#
+# default numerical definitions
+#
+$Extend       = [\p{Word_Break = Extend}];
+$Format       = [\p{Word_Break = Format}];
+$MidNumLet    = [\p{Word_Break = MidNumLet}];
+$MidNum       = [\p{Word_Break = MidNum}];
+$Numeric      = [\p{Word_Break = Numeric}];
+$ExtendNumLet = [\p{Word_Break = ExtendNumLet}];                                                          
+$MidNumLetEx    = $MidNumLet    ($Extend |  $Format)*;
+$MidNumEx       = $MidNum       ($Extend |  $Format)*;
+$NumericEx      = $Numeric      ($Extend |  $Format)*;
+$ExtendNumLetEx = $ExtendNumLet ($Extend |  $Format)*;
+
+$ConsEx = $Cons ($Extend | $Format)*;
+$AsatEx = $Cons $Asat ($Virama $ConsEx)? ($Extend | $Format)*;
+$MyanmarSyllableEx = $ConsEx ($Virama $ConsEx)? ($AsatEx)*;
+$MyanmarJoinedSyllableEx = $MyanmarSyllableEx ($WordJoin $MyanmarSyllableEx)*;
+
+!!forward;
+$MyanmarJoinedSyllableEx {200};
+
+# default numeric rules
+$NumericEx $ExtendNumLetEx? (($MidNumEx | $MidNumLetEx)? $NumericEx $ExtendNumLetEx?)*  {100};

lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/segmentation/DefaultICUTokenizerConfig.java

@@ -63,9 +63,12 @@ public class DefaultICUTokenizerConfig extends ICUTokenizerConfig {
   // the same as ROOT, except no dictionary segmentation for cjk
   private static final BreakIterator defaultBreakIterator = 
     readBreakIterator("Default.brk");
+  private static final BreakIterator myanmarSyllableIterator = 
+    readBreakIterator("MyanmarSyllable.brk");
   
   // TODO: deprecate this boolean? you only care if you are doing super-expert stuff...
   private final boolean cjkAsWords;
+  private final boolean myanmarAsWords;
   
   /** 
    * Creates a new config. This object is lightweight, but the first
@@ -74,9 +77,12 @@ public class DefaultICUTokenizerConfig extends ICUTokenizerConfig {
    *                   otherwise text will be segmented according to UAX#29 defaults.
    *                   If this is true, all Han+Hiragana+Katakana words will be tagged as
    *                   IDEOGRAPHIC.
+   * @param myanmarAsWords true if Myanmar text should undergo dictionary-based segmentation,
+   *                       otherwise it will be tokenized as syllables.
    */
-  public DefaultICUTokenizerConfig(boolean cjkAsWords) { 
+  public DefaultICUTokenizerConfig(boolean cjkAsWords, boolean myanmarAsWords) { 
     this.cjkAsWords = cjkAsWords;
+    this.myanmarAsWords = myanmarAsWords;
   }
   
   @Override
@@ -88,6 +94,12 @@ public class DefaultICUTokenizerConfig extends ICUTokenizerConfig {
   public BreakIterator getBreakIterator(int script) {
     switch(script) {
       case UScript.JAPANESE: return (BreakIterator)cjkBreakIterator.clone();
+      case UScript.MYANMAR: 
+        if (myanmarAsWords) {
+          return (BreakIterator)defaultBreakIterator.clone();
+        } else {
+          return (BreakIterator)myanmarSyllableIterator.clone();
+        }
       default: return (BreakIterator)defaultBreakIterator.clone();
     }
   }

lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/segmentation/ICUTokenizer.java

@@ -68,7 +68,7 @@ public final class ICUTokenizer extends Tokenizer {
    * @see DefaultICUTokenizerConfig
    */
   public ICUTokenizer() {
-    this(new DefaultICUTokenizerConfig(true));
+    this(new DefaultICUTokenizerConfig(true, true));
   }
 
   /**

lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/segmentation/ICUTokenizerFactory.java

@@ -79,6 +79,7 @@ public class ICUTokenizerFactory extends TokenizerFactory implements ResourceLoa
   private final Map<Integer,String> tailored;
   private ICUTokenizerConfig config;
   private final boolean cjkAsWords;
+  private final boolean myanmarAsWords;
   
   /** Creates a new ICUTokenizerFactory */
   public ICUTokenizerFactory(Map<String,String> args) {
@@ -95,6 +96,7 @@ public class ICUTokenizerFactory extends TokenizerFactory implements ResourceLoa
       }
     }
     cjkAsWords = getBoolean(args, "cjkAsWords", true);
+    myanmarAsWords = getBoolean(args, "myanmarAsWords", true);
     if (!args.isEmpty()) {
       throw new IllegalArgumentException("Unknown parameters: " + args);
     }
@@ -104,7 +106,7 @@ public class ICUTokenizerFactory extends TokenizerFactory implements ResourceLoa
   public void inform(ResourceLoader loader) throws IOException {
     assert tailored != null : "init must be called first!";
     if (tailored.isEmpty()) {
-      config = new DefaultICUTokenizerConfig(cjkAsWords);
+      config = new DefaultICUTokenizerConfig(cjkAsWords, myanmarAsWords);
     } else {
       final BreakIterator breakers[] = new BreakIterator[UScript.CODE_LIMIT];
       for (Map.Entry<Integer,String> entry : tailored.entrySet()) {
@@ -112,7 +114,7 @@ public class ICUTokenizerFactory extends TokenizerFactory implements ResourceLoa
         String resourcePath = entry.getValue();
         breakers[code] = parseRules(resourcePath, loader);
       }
-      config = new DefaultICUTokenizerConfig(cjkAsWords) {
+      config = new DefaultICUTokenizerConfig(cjkAsWords, myanmarAsWords) {
         
         @Override
         public BreakIterator getBreakIterator(int script) {

lucene/analysis/icu/src/test/org/apache/lucene/analysis/icu/segmentation/TestICUTokenizer.java

@@ -42,7 +42,7 @@ public class TestICUTokenizer extends BaseTokenStreamTestCase {
     sb.append(whitespace);
     sb.append("testing 1234");
     String input = sb.toString();
-    ICUTokenizer tokenizer = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false));
+    ICUTokenizer tokenizer = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false, true));
     tokenizer.setReader(new StringReader(input));
     assertTokenStreamContents(tokenizer, new String[] { "testing", "1234" });
   }
@@ -53,7 +53,7 @@ public class TestICUTokenizer extends BaseTokenStreamTestCase {
       sb.append('a');
     }
     String input = sb.toString();
-    ICUTokenizer tokenizer = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false));
+    ICUTokenizer tokenizer = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false, true));
     tokenizer.setReader(new StringReader(input));
     char token[] = new char[4096];
     Arrays.fill(token, 'a');
@@ -75,7 +75,7 @@ public class TestICUTokenizer extends BaseTokenStreamTestCase {
     a = new Analyzer() {
       @Override
       protected TokenStreamComponents createComponents(String fieldName) {
-        Tokenizer tokenizer = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false));
+        Tokenizer tokenizer = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false, true));
         TokenFilter filter = new ICUNormalizer2Filter(tokenizer);
         return new TokenStreamComponents(tokenizer, filter);
       }

lucene/analysis/icu/src/test/org/apache/lucene/analysis/icu/segmentation/TestICUTokenizerCJK.java

@@ -34,7 +34,7 @@ public class TestICUTokenizerCJK extends BaseTokenStreamTestCase {
     a = new Analyzer() {
       @Override
       protected TokenStreamComponents createComponents(String fieldName) {
-        return new TokenStreamComponents(new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(true)));
+        return new TokenStreamComponents(new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(true, true)));
       }
     };
   }

lucene/analysis/icu/src/test/org/apache/lucene/analysis/icu/segmentation/TestMyanmarSyllable.java

@@ -0,0 +1,156 @@
+/*
+ * 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.analysis.icu.segmentation;
+
+import org.apache.lucene.analysis.Analyzer;
+import org.apache.lucene.analysis.BaseTokenStreamTestCase;
+import org.apache.lucene.analysis.Tokenizer;
+
+/** Test tokenizing Myanmar text into syllables */
+public class TestMyanmarSyllable extends BaseTokenStreamTestCase {
+
+  Analyzer a;
+
+  @Override
+  public void setUp() throws Exception {
+    super.setUp();
+    a = new Analyzer() {
+      @Override
+      protected TokenStreamComponents createComponents(String fieldName) {
+        Tokenizer tokenizer = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false, false));
+        return new TokenStreamComponents(tokenizer);
+      }
+    };
+  }
+  
+  @Override
+  public void tearDown() throws Exception {
+    a.close();
+    super.tearDown();
+  }
+  
+  /** as opposed to dictionary break of သက်ဝင်|လှုပ်ရှား|စေ|ပြီး */
+  public void testBasics() throws Exception {
+    assertAnalyzesTo(a, "သက်ဝင်လှုပ်ရှားစေပြီး", new String[] { "သက်", "ဝင်", "လှုပ်", "ရှား", "စေ", "ပြီး" });
+  }
+  
+  // simple tests from "A Rule-based Syllable Segmentation of Myanmar Text" 
+  // * http://www.aclweb.org/anthology/I08-3010
+  // (see also the presentation: http://gii2.nagaokaut.ac.jp/gii/media/share/20080901-ZMM%20Presentation.pdf)
+  // The words are fake, we just test the categories.
+  // note that currently our algorithm is not sophisticated enough to handle some of the special cases!
+  
+  /** constant */
+  public void testC() throws Exception {
+    assertAnalyzesTo(a, "ကက", new String[] { "က", "က" });
+  }
+  
+  /** consonant + sign */
+  public void testCF() throws Exception {
+    assertAnalyzesTo(a, "ကံကံ", new String[] { "ကံ", "ကံ" });
+  }
+  
+  /** consonant + consonant + asat */
+  public void testCCA() throws Exception {
+    assertAnalyzesTo(a, "ကင်ကင်", new String[] { "ကင်", "ကင်" });
+  }
+  
+  /** consonant + consonant + asat + sign */
+  public void testCCAF() throws Exception {
+    assertAnalyzesTo(a, "ကင်းကင်း", new String[] { "ကင်း", "ကင်း" });
+  }
+  
+  /** consonant + vowel */
+  public void testCV() throws Exception {
+    assertAnalyzesTo(a, "ကာကာ", new String[] { "ကာ", "ကာ" });
+  }
+  
+  /** consonant + vowel + sign */
+  public void testCVF() throws Exception {
+    assertAnalyzesTo(a, "ကားကား", new String[] { "ကား", "ကား" });
+  }
+  
+  /** consonant + vowel + vowel + asat */
+  public void testCVVA() throws Exception {
+    assertAnalyzesTo(a, "ကော်ကော်", new String[] { "ကော်", "ကော်" });
+  }
+  
+  /** consonant + vowel + vowel + consonant + asat */
+  public void testCVVCA() throws Exception {
+    assertAnalyzesTo(a, "ကောင်ကောင်", new String[] { "ကောင်", "ကောင်" });
+  }
+  
+  /** consonant + vowel + vowel + consonant + asat + sign */
+  public void testCVVCAF() throws Exception {
+    assertAnalyzesTo(a, "ကောင်းကောင်း", new String[] { "ကောင်း", "ကောင်း" });
+  }
+  
+  /** consonant + medial */
+  public void testCM() throws Exception {
+    assertAnalyzesTo(a, "ကျကျ", new String[] { "ကျ", "ကျ" });
+  }
+  
+  /** consonant + medial + sign */
+  public void testCMF() throws Exception {
+    assertAnalyzesTo(a, "ကျံကျံ", new String[] { "ကျံ", "ကျံ" });
+  }
+  
+  /** consonant + medial + consonant + asat */
+  public void testCMCA() throws Exception {
+    assertAnalyzesTo(a, "ကျင်ကျင်", new String[] { "ကျင်", "ကျင်" });
+  }
+  
+  /** consonant + medial + consonant + asat + sign */
+  public void testCMCAF() throws Exception {
+    assertAnalyzesTo(a, "ကျင်းကျင်း", new String[] { "ကျင်း", "ကျင်း" });
+  }
+  
+  /** consonant + medial + vowel */
+  public void testCMV() throws Exception {
+    assertAnalyzesTo(a, "ကျာကျာ", new String[] { "ကျာ", "ကျာ" });
+  }
+  
+  /** consonant + medial + vowel + sign */
+  public void testCMVF() throws Exception {
+    assertAnalyzesTo(a, "ကျားကျား", new String[] { "ကျား", "ကျား" });
+  }
+  
+  /** consonant + medial + vowel + vowel + asat */
+  public void testCMVVA() throws Exception {
+    assertAnalyzesTo(a, "ကျော်ကျော်", new String[] { "ကျော်", "ကျော်" });
+  }
+  
+  /** consonant + medial + vowel + vowel + consonant + asat */
+  public void testCMVVCA() throws Exception {
+    assertAnalyzesTo(a, "ကြောင်ကြောင်", new String[] { "ကြောင်", "ကြောင်"});
+  }
+  
+  /** consonant + medial + vowel + vowel + consonant + asat + sign */
+  public void testCMVVCAF() throws Exception {
+    assertAnalyzesTo(a, "ကြောင်းကြောင်း", new String[] { "ကြောင်း", "ကြောင်း"});
+  }
+  
+  /** independent vowel */
+  public void testI() throws Exception {
+    assertAnalyzesTo(a, "ဪဪ", new String[] { "ဪ", "ဪ" });
+  }
+  
+  /** independent vowel */
+  public void testE() throws Exception {
+    assertAnalyzesTo(a, "ဣဣ", new String[] { "ဣ", "ဣ" });
+  }
+}

lucene/analysis/icu/src/test/org/apache/lucene/analysis/icu/segmentation/TestWithCJKBigramFilter.java

@@ -46,7 +46,7 @@ public class TestWithCJKBigramFilter extends BaseTokenStreamTestCase {
     analyzer = new Analyzer() {
       @Override
       protected TokenStreamComponents createComponents(String fieldName) {
-        Tokenizer source = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false));
+        Tokenizer source = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false, true));
         TokenStream result = new CJKBigramFilter(source);
         return new TokenStreamComponents(source, new StopFilter(result, CharArraySet.EMPTY_SET));
       }
@@ -60,7 +60,7 @@ public class TestWithCJKBigramFilter extends BaseTokenStreamTestCase {
     analyzer2 = new Analyzer() {
       @Override
       protected TokenStreamComponents createComponents(String fieldName) {
-        Tokenizer source = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false));
+        Tokenizer source = new ICUTokenizer(newAttributeFactory(), new DefaultICUTokenizerConfig(false, true));
         // we put this before the CJKBigramFilter, because the normalization might combine
         // some halfwidth katakana forms, which will affect the bigramming.
         TokenStream result = new ICUNormalizer2Filter(source);

lucene/classification/src/java/org/apache/lucene/classification/utils/DatasetSplitter.java

@@ -30,6 +30,7 @@ import org.apache.lucene.index.IndexWriterConfig;
 import org.apache.lucene.index.IndexableField;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.SortedDocValues;
+import org.apache.lucene.index.SortedSetDocValues;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.ScoreDoc;
@@ -82,11 +83,20 @@ public class DatasetSplitter {
     // get the exact no. of existing classes
     int noOfClasses = 0;
     for (LeafReaderContext leave : originalIndex.leaves()) {
+      long valueCount = 0;
       SortedDocValues classValues = leave.reader().getSortedDocValues(classFieldName);
-      if (classValues == null) {
-        throw new IllegalStateException("the classFieldName \"" + classFieldName + "\" must index sorted doc values");
+      if (classValues != null) {
+        valueCount = classValues.getValueCount();
+      } else {
+        SortedSetDocValues sortedSetDocValues = leave.reader().getSortedSetDocValues(classFieldName);
+        if (sortedSetDocValues != null) {
+          valueCount = sortedSetDocValues.getValueCount();
         }
-      noOfClasses += classValues.getValueCount();
+      }
+      if (classValues == null) {
+        throw new IllegalStateException("field \"" + classFieldName + "\" must have sorted (set) doc values");
+      }
+      noOfClasses += valueCount;
     }
 
     try {

lucene/codecs/src/java/org/apache/lucene/codecs/simpletext/SimpleTextPointsWriter.java

@@ -68,7 +68,7 @@ class SimpleTextPointsWriter extends PointsWriter {
   }
 
   @Override
-  public void writeField(FieldInfo fieldInfo, PointsReader values, double maxMBSortInHeap) throws IOException {
+  public void writeField(FieldInfo fieldInfo, PointsReader values) throws IOException {
 
     boolean singleValuePerDoc = values.size(fieldInfo.name) == values.getDocCount(fieldInfo.name);
 
@@ -79,7 +79,7 @@ class SimpleTextPointsWriter extends PointsWriter {
                                           fieldInfo.getPointDimensionCount(),
                                           fieldInfo.getPointNumBytes(),
                                           BKDWriter.DEFAULT_MAX_POINTS_IN_LEAF_NODE,
-                                          maxMBSortInHeap,
+                                          BKDWriter.DEFAULT_MAX_MB_SORT_IN_HEAP,
                                           values.size(fieldInfo.name),
                                           singleValuePerDoc) {
 

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

@@ -0,0 +1,41 @@
+/*
+ * 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;
+
+import org.apache.lucene.util.BytesRef;
+
+/** {@link PointsReader} whose order of points can be changed.
+ *  This class is useful for codecs to optimize flush.
+ *  @lucene.internal */
+public abstract class MutablePointsReader extends PointsReader {
+
+  /** Sole constructor. */
+  protected MutablePointsReader() {}
+
+  /** Set {@code packedValue} with a reference to the packed bytes of the i-th value. */
+  public abstract void getValue(int i, BytesRef packedValue);
+
+  /** Get the k-th byte of the i-th value. */
+  public abstract byte getByteAt(int i, int k);
+
+  /** Return the doc ID of the i-th value. */
+  public abstract int getDocID(int i);
+
+  /** Swap the i-th and j-th values. */
+  public abstract void swap(int i, int j);
+
+}

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

@@ -22,7 +22,6 @@ import java.io.IOException;
 
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.MergeState;
-import org.apache.lucene.util.bkd.BKDWriter;
 
 /** Abstract API to write points
  *
@@ -35,9 +34,8 @@ public abstract class PointsWriter implements Closeable {
   protected PointsWriter() {
   }
 
-  /** Write all values contained in the provided reader.  {@code maxMBSortInHeap} is the maximum
-   *  transient heap that can be used to sort values, before spilling to disk for offline sorting */
-  public abstract void writeField(FieldInfo fieldInfo, PointsReader values, double maxMBSortInHeap) throws IOException;
+  /** Write all values contained in the provided reader */
+  public abstract void writeField(FieldInfo fieldInfo, PointsReader values) throws IOException;
 
   /** Default naive merge implementation for one field: it just re-indexes all the values
    *  from the incoming segment.  The default codec overrides this for 1D fields and uses
@@ -147,10 +145,7 @@ public abstract class PointsWriter implements Closeable {
                  public int getDocCount(String fieldName) {
                    return finalDocCount;
                  }
-               },
-               // TODO: also let merging of > 1D fields tap into IW's indexing buffer size, somehow (1D fields do an optimized merge sort
-               // and don't need heap)
-               BKDWriter.DEFAULT_MAX_MB_SORT_IN_HEAP);
+               });
   }
 
   /** Default merge implementation to merge incoming points readers by visiting all their points and

lucene/core/src/java/org/apache/lucene/codecs/lucene60/Lucene60PointsWriter.java

@@ -25,6 +25,7 @@ import java.util.List;
 import java.util.Map;
 
 import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.MutablePointsReader;
 import org.apache.lucene.codecs.PointsReader;
 import org.apache.lucene.codecs.PointsWriter;
 import org.apache.lucene.index.FieldInfo;
@@ -39,9 +40,7 @@ import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.bkd.BKDReader;
 import org.apache.lucene.util.bkd.BKDWriter;
 
-/** Writes dimensional values
- *
- * @lucene.experimental */
+/** Writes dimensional values */
 public class Lucene60PointsWriter extends PointsWriter implements Closeable {
 
   /** Output used to write the BKD tree data file */
@@ -52,13 +51,15 @@ public class Lucene60PointsWriter extends PointsWriter implements Closeable {
 
   final SegmentWriteState writeState;
   final int maxPointsInLeafNode;
+  final double maxMBSortInHeap;
   private boolean finished;
 
   /** Full constructor */
-  public Lucene60PointsWriter(SegmentWriteState writeState, int maxPointsInLeafNode) throws IOException {
+  public Lucene60PointsWriter(SegmentWriteState writeState, int maxPointsInLeafNode, double maxMBSortInHeap) throws IOException {
     assert writeState.fieldInfos.hasPointValues();
     this.writeState = writeState;
     this.maxPointsInLeafNode = maxPointsInLeafNode;
+    this.maxMBSortInHeap = maxMBSortInHeap;
     String dataFileName = IndexFileNames.segmentFileName(writeState.segmentInfo.name,
                                                          writeState.segmentSuffix,
                                                          Lucene60PointsFormat.DATA_EXTENSION);
@@ -80,11 +81,11 @@ public class Lucene60PointsWriter extends PointsWriter implements Closeable {
 
   /** Uses the defaults values for {@code maxPointsInLeafNode} (1024) and {@code maxMBSortInHeap} (16.0) */
   public Lucene60PointsWriter(SegmentWriteState writeState) throws IOException {
-    this(writeState, BKDWriter.DEFAULT_MAX_POINTS_IN_LEAF_NODE);
+    this(writeState, BKDWriter.DEFAULT_MAX_POINTS_IN_LEAF_NODE, BKDWriter.DEFAULT_MAX_MB_SORT_IN_HEAP);
   }
 
   @Override
-  public void writeField(FieldInfo fieldInfo, PointsReader values, double maxMBSortInHeap) throws IOException {
+  public void writeField(FieldInfo fieldInfo, PointsReader values) throws IOException {
 
     boolean singleValuePerDoc = values.size(fieldInfo.name) == values.getDocCount(fieldInfo.name);
 
@@ -98,6 +99,14 @@ public class Lucene60PointsWriter extends PointsWriter implements Closeable {
                                           values.size(fieldInfo.name),
                                           singleValuePerDoc)) {
 
+      if (values instanceof MutablePointsReader) {
+        final long fp = writer.writeField(dataOut, fieldInfo.name, (MutablePointsReader) values);
+        if (fp != -1) {
+          indexFPs.put(fieldInfo.name, fp);
+        }
+        return;
+      }
+
       values.intersect(fieldInfo.name, new IntersectVisitor() {
           @Override
           public void visit(int docID) {
@@ -173,8 +182,7 @@ public class Lucene60PointsWriter extends PointsWriter implements Closeable {
                                                 fieldInfo.getPointDimensionCount(),
                                                 fieldInfo.getPointNumBytes(),
                                                 maxPointsInLeafNode,
-                                                // NOTE: not used, since BKDWriter.merge does a merge sort:
-                                                BKDWriter.DEFAULT_MAX_MB_SORT_IN_HEAP,
+                                                maxMBSortInHeap,
                                                 totMaxSize,
                                                 singleValuePerDoc)) {
             List<BKDReader> bkdReaders = new ArrayList<>();

lucene/core/src/java/org/apache/lucene/document/Field.java

@@ -257,7 +257,7 @@ public class Field implements IndexableField {
   /**
    * The value of the field as a String, or null. If null, the Reader value or
    * binary value is used. Exactly one of stringValue(), readerValue(), and
-   * getBinaryValue() must be set.
+   * binaryValue() must be set.
    */
   @Override
   public String stringValue() {
@@ -271,7 +271,7 @@ public class Field implements IndexableField {
   /**
    * The value of the field as a Reader, or null. If null, the String value or
    * binary value is used. Exactly one of stringValue(), readerValue(), and
-   * getBinaryValue() must be set.
+   * binaryValue() must be set.
    */
   @Override
   public Reader readerValue() {
@@ -420,7 +420,7 @@ public class Field implements IndexableField {
   /**
    * Expert: sets the token stream to be used for indexing and causes
    * isIndexed() and isTokenized() to return true. May be combined with stored
-   * values from stringValue() or getBinaryValue()
+   * values from stringValue() or binaryValue()
    */
   public void setTokenStream(TokenStream tokenStream) {
     if (type.indexOptions() == IndexOptions.NONE || !type.tokenized()) {

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

@@ -153,7 +153,7 @@ class DocumentsWriterPerThread {
   final Allocator byteBlockAllocator;
   final IntBlockPool.Allocator intBlockAllocator;
   private final AtomicLong pendingNumDocs;
-  final LiveIndexWriterConfig indexWriterConfig;
+  private final LiveIndexWriterConfig indexWriterConfig;
   private final boolean enableTestPoints;
   private final IndexWriter indexWriter;
   

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

@@ -762,7 +762,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
    * {@link #getConfig()}.
    * 
    * <p>
-   * <b>NOTE:</b> after this writer is created, the given configuration instance
+   * <b>NOTE:</b> after ths writer is created, the given configuration instance
    * cannot be passed to another writer.
    * 
    * @param d

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

@@ -168,14 +168,9 @@ public class LiveIndexWriterConfig {
   
   /**
    * Determines the amount of RAM that may be used for buffering added documents
-   * and deletions before beginning to flush them to the Directory.  For
-   * faster indexing performance it's best to use as large a RAM buffer as you can.
-   * <p>
-   * Note that this setting is not a hard limit on memory usage during indexing, as
-   * transient and non-trivial memory well beyond this buffer size may be used,
-   * for example due to segment merges or writing points to new segments.
-   * For application stability the available memory in the JVM
-   * should be significantly larger than the RAM buffer used for indexing.
+   * and deletions before they are flushed to the Directory. Generally for
+   * faster indexing performance it's best to flush by RAM usage instead of
+   * document count and use as large a RAM buffer as you can.
    * <p>
    * When this is set, the writer will flush whenever buffered documents and
    * deletions use this much RAM. Pass in
@@ -183,6 +178,14 @@ public class LiveIndexWriterConfig {
    * due to RAM usage. Note that if flushing by document count is also enabled,
    * then the flush will be triggered by whichever comes first.
    * <p>
+   * The maximum RAM limit is inherently determined by the JVMs available
+   * memory. Yet, an {@link IndexWriter} session can consume a significantly
+   * larger amount of memory than the given RAM limit since this limit is just
+   * an indicator when to flush memory resident documents to the Directory.
+   * Flushes are likely happen concurrently while other threads adding documents
+   * to the writer. For application stability the available memory in the JVM
+   * should be significantly larger than the RAM buffer used for indexing.
+   * <p>
    * <b>NOTE</b>: the account of RAM usage for pending deletions is only
    * approximate. Specifically, if you delete by Query, Lucene currently has no
    * way to measure the RAM usage of individual Queries so the accounting will

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

@@ -18,13 +18,13 @@ package org.apache.lucene.index;
 
 import java.io.IOException;
 
+import org.apache.lucene.codecs.MutablePointsReader;
 import org.apache.lucene.codecs.PointsReader;
 import org.apache.lucene.codecs.PointsWriter;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.ByteBlockPool;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.Counter;
-import org.apache.lucene.util.bkd.BKDWriter;
 
 /** Buffers up pending byte[][] value(s) per doc, then flushes when segment flushes. */
 class PointValuesWriter {
@@ -35,8 +35,7 @@ class PointValuesWriter {
   private int numPoints;
   private int numDocs;
   private int lastDocID = -1;
-  private final byte[] packedValue;
-  private final LiveIndexWriterConfig indexWriterConfig;
+  private final int packedBytesLength;
 
   public PointValuesWriter(DocumentsWriterPerThread docWriter, FieldInfo fieldInfo) {
     this.fieldInfo = fieldInfo;
@@ -44,8 +43,7 @@ class PointValuesWriter {
     this.bytes = new ByteBlockPool(docWriter.byteBlockAllocator);
     docIDs = new int[16];
     iwBytesUsed.addAndGet(16 * Integer.BYTES);
-    packedValue = new byte[fieldInfo.getPointDimensionCount() * fieldInfo.getPointNumBytes()];
-    indexWriterConfig = docWriter.indexWriterConfig;
+    packedBytesLength = fieldInfo.getPointDimensionCount() * fieldInfo.getPointNumBytes();
   }
 
   // TODO: if exactly the same value is added to exactly the same doc, should we dedup?
@@ -53,9 +51,10 @@ class PointValuesWriter {
     if (value == null) {
       throw new IllegalArgumentException("field=" + fieldInfo.name + ": point value must not be null");
     }
-    if (value.length != fieldInfo.getPointDimensionCount() * fieldInfo.getPointNumBytes()) {
+    if (value.length != packedBytesLength) {
       throw new IllegalArgumentException("field=" + fieldInfo.name + ": this field's value has length=" + value.length + " but should be " + (fieldInfo.getPointDimensionCount() * fieldInfo.getPointNumBytes()));
     }
+
     if (docIDs.length == numPoints) {
       docIDs = ArrayUtil.grow(docIDs, numPoints+1);
       iwBytesUsed.addAndGet((docIDs.length - numPoints) * Integer.BYTES);
@@ -66,21 +65,32 @@ class PointValuesWriter {
       numDocs++;
       lastDocID = docID;
     }
+
     numPoints++;
   }
 
   public void flush(SegmentWriteState state, PointsWriter writer) throws IOException {
+    PointsReader reader = new MutablePointsReader() {
+
+      final int[] ords = new int[numPoints];
+      {
+        for (int i = 0; i < numPoints; ++i) {
+          ords[i] = i;
+        }
+      }
 
-    writer.writeField(fieldInfo,
-                      new PointsReader() {
       @Override
       public void intersect(String fieldName, IntersectVisitor visitor) throws IOException {
         if (fieldName.equals(fieldInfo.name) == false) {
           throw new IllegalArgumentException("fieldName must be the same");
         }
+        final BytesRef scratch = new BytesRef();
+        final byte[] packedValue = new byte[packedBytesLength];
         for(int i=0;i<numPoints;i++) {
-                            bytes.readBytes(packedValue.length * i, packedValue, 0, packedValue.length);
-                            visitor.visit(docIDs[i], packedValue);
+          getValue(i, scratch);
+          assert scratch.length == packedValue.length;
+          System.arraycopy(scratch.bytes, scratch.offset, packedValue, 0, packedBytesLength);
+          visitor.visit(getDocID(i), packedValue);
         }
       }
 
@@ -120,14 +130,46 @@ class PointValuesWriter {
 
       @Override
       public long size(String fieldName) {
+        if (fieldName.equals(fieldInfo.name) == false) {
+          throw new IllegalArgumentException("fieldName must be the same");
+        }
         return numPoints;
       }
 
       @Override
       public int getDocCount(String fieldName) {
+        if (fieldName.equals(fieldInfo.name) == false) {
+          throw new IllegalArgumentException("fieldName must be the same");
+        }
         return numDocs;
       }
-                      },
-                      Math.max(indexWriterConfig.getRAMBufferSizeMB()/8.0, BKDWriter.DEFAULT_MAX_MB_SORT_IN_HEAP));
+
+      @Override
+      public void swap(int i, int j) {
+        int tmp = ords[i];
+        ords[i] = ords[j];
+        ords[j] = tmp;
+      }
+
+      @Override
+      public int getDocID(int i) {
+        return docIDs[ords[i]];
+      }
+
+      @Override
+      public void getValue(int i, BytesRef packedValue) {
+        final long offset = (long) packedBytesLength * ords[i];
+        packedValue.length = packedBytesLength;
+        bytes.setRawBytesRef(packedValue, offset);
+      }
+
+      @Override
+      public byte getByteAt(int i, int k) {
+        final long offset = (long) packedBytesLength * ords[i] + k;
+        return bytes.readByte(offset);
+      }
+    };
+
+    writer.writeField(fieldInfo, reader);
   }
 }

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

@@ -405,6 +405,7 @@ public class LRUQueryCache implements QueryCache, Accountable {
     lock.lock();
     try {
       cache.clear();
+      // Note that this also clears the uniqueQueries map since mostRecentlyUsedQueries is the uniqueQueries.keySet view:
       mostRecentlyUsedQueries.clear();
       onClear();
     } finally {

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

@@ -41,7 +41,8 @@ public class PrefixQuery extends AutomatonQuery {
 
   /** Build an automaton accepting all terms with the specified prefix. */
   public static Automaton toAutomaton(BytesRef prefix) {
-    Automaton automaton = new Automaton();
+    final int numStatesAndTransitions = prefix.length+1;
+    final Automaton automaton = new Automaton(numStatesAndTransitions, numStatesAndTransitions);
     int lastState = automaton.createState();
     for(int i=0;i<prefix.length;i++) {
       int state = automaton.createState();
@@ -66,7 +67,7 @@ public class PrefixQuery extends AutomatonQuery {
     StringBuilder buffer = new StringBuilder();
     if (!getField().equals(field)) {
       buffer.append(getField());
-      buffer.append(":");
+      buffer.append(':');
     }
     buffer.append(term.text());
     buffer.append('*');

lucene/core/src/java/org/apache/lucene/util/ArrayUtil.java

@@ -459,69 +459,26 @@ public final class ArrayUtil {
    *  greater than or equal to it.
    *  This runs in linear time on average and in {@code n log(n)} time in the
    *  worst case.*/
-  public static <T> void select(T[] arr, int from, int to, int k, Comparator<T> comparator) {
-    if (k < from) {
-      throw new IllegalArgumentException("k must be >= from");
-    }
-    if (k >= to) {
-      throw new IllegalArgumentException("k must be < to");
-    }
-    final int maxDepth = 2 * MathUtil.log(to - from, 2);
-    quickSelect(arr, from, to, k, comparator, maxDepth);
+  public static <T> void select(T[] arr, int from, int to, int k, Comparator<? super T> comparator) {
+    new IntroSelector() {
+
+      T pivot;
+
+      @Override
+      protected void swap(int i, int j) {
+        ArrayUtil.swap(arr, i, j);
       }
 
-  private static <T> void quickSelect(T[] arr, int from, int to, int k, Comparator<T> comparator, int maxDepth) {
-    assert from <= k;
-    assert k < to;
-    if (to - from == 1) {
-      return;
-    }
-    if (--maxDepth < 0) {
-      Arrays.sort(arr, from, to, comparator);
-      return;
+      @Override
+      protected void setPivot(int i) {
+        pivot = arr[i];
       }
 
-    final int mid = (from + to) >>> 1;
-    // heuristic: we use the median of the values at from, to-1 and mid as a pivot
-    if (comparator.compare(arr[from], arr[to - 1]) > 0) {
-      swap(arr, from, to - 1);
-    }
-    if (comparator.compare(arr[to - 1], arr[mid]) > 0) {
-      swap(arr, to - 1, mid);
-      if (comparator.compare(arr[from], arr[to - 1]) > 0) {
-        swap(arr, from, to - 1);
+      @Override
+      protected int comparePivot(int j) {
+        return comparator.compare(pivot, arr[j]);
       }
+    }.select(from, to, k);
   }
 
-    T pivot = arr[to - 1];
-
-    int left = from + 1;
-    int right = to - 2;
-
-    for (;;) {
-      while (comparator.compare(pivot, arr[left]) > 0) {
-        ++left;
-      }
-
-      while (left < right && comparator.compare(pivot, arr[right]) <= 0) {
-        --right;
-      }
-
-      if (left < right) {
-        swap(arr, left, right);
-        --right;
-      } else {
-        break;
-      }
-    }
-    swap(arr, left, to - 1);
-
-    if (left == k) {
-      return;
-    } else if (left < k) {
-      quickSelect(arr, left + 1, to, k, comparator, maxDepth);
-    } else {
-      quickSelect(arr, from, left, k, comparator, maxDepth);
-    }
-  }
 }

lucene/core/src/java/org/apache/lucene/util/ByteBlockPool.java

@@ -378,5 +378,34 @@ public final class ByteBlockPool {
       }
     } while (true);
   }
+
+  /**
+   * Set the given {@link BytesRef} so that its content is equal to the
+   * {@code ref.length} bytes starting at {@code offset}. Most of the time this
+   * method will set pointers to internal data-structures. However, in case a
+   * value crosses a boundary, a fresh copy will be returned.
+   * On the contrary to {@link #setBytesRef(BytesRef, int)}, this does not
+   * expect the length to be encoded with the data.
+   */
+  public void setRawBytesRef(BytesRef ref, final long offset) {
+    int bufferIndex = (int) (offset >> BYTE_BLOCK_SHIFT);
+    int pos = (int) (offset & BYTE_BLOCK_MASK);
+    if (pos + ref.length <= BYTE_BLOCK_SIZE) {
+      ref.bytes = buffers[bufferIndex];
+      ref.offset = pos;
+    } else {
+      ref.bytes = new byte[ref.length];
+      ref.offset = 0;
+      readBytes(offset, ref.bytes, 0, ref.length);
+    }
+  }
+
+  /** Read a single byte at the given {@code offset}. */
+  public byte readByte(long offset) {
+    int bufferIndex = (int) (offset >> BYTE_BLOCK_SHIFT);
+    int pos = (int) (offset & BYTE_BLOCK_MASK);
+    byte[] buffer = buffers[bufferIndex];
+    return buffer[pos];
+  }
 }
 

lucene/core/src/java/org/apache/lucene/util/InPlaceMergeSorter.java

@@ -33,8 +33,8 @@ public abstract class InPlaceMergeSorter extends Sorter {
   }
 
   void mergeSort(int from, int to) {
-    if (to - from < INSERTION_SORT_THRESHOLD) {
-      insertionSort(from, to);
+    if (to - from < BINARY_SORT_THRESHOLD) {
+      binarySort(from, to);
     } else {
       final int mid = (from + to) >>> 1;
       mergeSort(from, mid);

lucene/core/src/java/org/apache/lucene/util/IntroSelector.java

@@ -0,0 +1,128 @@
+/*
+ * 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.util;
+
+import java.util.Comparator;
+
+/** Implementation of the quick select algorithm.
+ *  <p>It uses the median of the first, middle and last values as a pivot and
+ *  falls back to a heap sort when the number of recursion levels exceeds
+ *  {@code 2 lg(n)}, as a consequence it runs in linear time on average and in
+ *  {@code n log(n)} time in the worst case.</p>
+ *  @lucene.internal */
+public abstract class IntroSelector extends Selector {
+
+  @Override
+  public final void select(int from, int to, int k) {
+    checkArgs(from, to, k);
+    final int maxDepth = 2 * MathUtil.log(to - from, 2);
+    quickSelect(from, to, k, maxDepth);
+  }
+
+  // heap sort
+  // TODO: use median of median instead to have linear worst-case rather than
+  // n*log(n)
+  void slowSelect(int from, int to, int k) {
+    new Sorter() {
+
+      @Override
+      protected void swap(int i, int j) {
+        IntroSelector.this.swap(i, j);
+      }
+
+      @Override
+      protected int compare(int i, int j) {
+        return IntroSelector.this.compare(i, j);
+      }
+
+      public void sort(int from, int to) {
+        heapSort(from, to);
+      }
+    }.sort(from, to);
+  }
+
+  private void quickSelect(int from, int to, int k, int maxDepth) {
+    assert from <= k;
+    assert k < to;
+    if (to - from == 1) {
+      return;
+    }
+    if (--maxDepth < 0) {
+      slowSelect(from, to, k);
+      return;
+    }
+
+    final int mid = (from + to) >>> 1;
+    // heuristic: we use the median of the values at from, to-1 and mid as a pivot
+    if (compare(from, to - 1) > 0) {
+      swap(from, to - 1);
+    }
+    if (compare(to - 1, mid) > 0) {
+      swap(to - 1, mid);
+      if (compare(from, to - 1) > 0) {
+        swap(from, to - 1);
+      }
+    }
+
+    setPivot(to - 1);
+
+    int left = from + 1;
+    int right = to - 2;
+
+    for (;;) {
+      while (comparePivot(left) > 0) {
+        ++left;
+      }
+
+      while (left < right && comparePivot(right) <= 0) {
+        --right;
+      }
+
+      if (left < right) {
+        swap(left, right);
+        --right;
+      } else {
+        break;
+      }
+    }
+    swap(left, to - 1);
+
+    if (left == k) {
+      return;
+    } else if (left < k) {
+      quickSelect(left + 1, to, k, maxDepth);
+    } else {
+      quickSelect(from, left, k, maxDepth);
+    }
+  }
+
+  /** Compare entries found in slots <code>i</code> and <code>j</code>.
+   *  The contract for the returned value is the same as
+   *  {@link Comparator#compare(Object, Object)}. */
+  protected int compare(int i, int j) {
+    setPivot(i);
+    return comparePivot(j);
+  }
+
+  /** Save the value at slot <code>i</code> so that it can later be used as a
+   * pivot, see {@link #comparePivot(int)}. */
+  protected abstract void setPivot(int i);
+
+  /** Compare the pivot with the slot at <code>j</code>, similarly to
+   *  {@link #compare(int, int) compare(i, j)}. */
+  protected abstract int comparePivot(int j);
+}

lucene/core/src/java/org/apache/lucene/util/IntroSorter.java

@@ -16,7 +16,6 @@
  */
 package org.apache.lucene.util;
 
-
 /**
  * {@link Sorter} implementation based on a variant of the quicksort algorithm
  * called <a href="http://en.wikipedia.org/wiki/Introsort">introsort</a>: when
@@ -38,8 +37,8 @@ public abstract class IntroSorter extends Sorter {
   }
 
   void quicksort(int from, int to, int maxDepth) {
-    if (to - from < INSERTION_SORT_THRESHOLD) {
-      insertionSort(from, to);
+    if (to - from < BINARY_SORT_THRESHOLD) {
+      binarySort(from, to);
       return;
     } else if (--maxDepth < 0) {
       heapSort(from, to);
@@ -84,11 +83,18 @@ public abstract class IntroSorter extends Sorter {
     quicksort(left + 1, to, maxDepth);
   }
 
-  /** Save the value at slot <code>i</code> so that it can later be used as a
-   * pivot, see {@link #comparePivot(int)}. */
+  // Don't rely on the slow default impl of setPivot/comparePivot since
+  // quicksort relies on these methods to be fast for good performance
+
+  @Override
   protected abstract void setPivot(int i);
 
-  /** Compare the pivot with the slot at <code>j</code>, similarly to
-   *  {@link #compare(int, int) compare(i, j)}. */
+  @Override
   protected abstract int comparePivot(int j);
+
+  @Override
+  protected int compare(int i, int j) {
+    setPivot(i);
+    return comparePivot(j);
+  }
 }

lucene/core/src/java/org/apache/lucene/util/MSBRadixSorter.java

@@ -38,6 +38,7 @@ public abstract class MSBRadixSorter extends Sorter {
   // we store one histogram per recursion level
   private final int[][] histograms = new int[LEVEL_THRESHOLD][];
   private final int[] endOffsets = new int[HISTOGRAM_SIZE];
+  private final int[] commonPrefix;
 
   private final int maxLength;
 
@@ -47,6 +48,7 @@ public abstract class MSBRadixSorter extends Sorter {
    */
   protected MSBRadixSorter(int maxLength) {
     this.maxLength = maxLength;
+    this.commonPrefix = new int[Math.min(24, maxLength)];
   }
 
   /** Return the k-th byte of the entry at index {@code i}, or {@code -1} if
@@ -116,14 +118,14 @@ public abstract class MSBRadixSorter extends Sorter {
   @Override
   public void sort(int from, int to) {
     checkRange(from, to);
-    sort(from, to, 0);
+    sort(from, to, 0, 0);
   }
 
-  private void sort(int from, int to, int k) {
-    if (to - from <= LENGTH_THRESHOLD || k >= LEVEL_THRESHOLD) {
+  private void sort(int from, int to, int k, int l) {
+    if (to - from <= LENGTH_THRESHOLD || l >= LEVEL_THRESHOLD) {
       introSort(from, to, k);
     } else {
-      radixSort(from, to, k);
+      radixSort(from, to, k, l);
     }
   }
 
@@ -131,28 +133,30 @@ public abstract class MSBRadixSorter extends Sorter {
     getFallbackSorter(k).sort(from, to);
   }
 
-  private void radixSort(int from, int to, int k) {
-    int[] histogram = histograms[k];
+  /**
+   * @param k the character number to compare
+   * @param l the level of recursion
+   */
+  private void radixSort(int from, int to, int k, int l) {
+    int[] histogram = histograms[l];
     if (histogram == null) {
-      histogram = histograms[k] = new int[HISTOGRAM_SIZE];
+      histogram = histograms[l] = new int[HISTOGRAM_SIZE];
     } else {
       Arrays.fill(histogram, 0);
     }
 
-    buildHistogram(from, to, k, histogram);
-
-    // short-circuit: if all keys have the same byte at offset k, then recurse directly
-    for (int i = 0; i < HISTOGRAM_SIZE; ++i) {
-      if (histogram[i] == to - from) {
-        // everything is in the same bucket, recurse
-        if (i > 0) {
-          sort(from, to, k + 1);
+    final int commonPrefixLength = computeCommonPrefixLengthAndBuildHistogram(from, to, k, histogram);
+    if (commonPrefixLength > 0) {
+      // if there are no more chars to compare or if all entries fell into the
+      // first bucket (which means strings are shorter than k) then we are done
+      // otherwise recurse
+      if (k + commonPrefixLength < maxLength
+          && histogram[0] < to - from) {
+        radixSort(from, to, k + commonPrefixLength, l);
       }
       return;
-      } else if (histogram[i] != 0) {
-        break;
-      }
     }
+    assert assertHistogram(commonPrefixLength, histogram);
 
     int[] startOffsets = histogram;
     int[] endOffsets = this.endOffsets;
@@ -167,24 +171,83 @@ public abstract class MSBRadixSorter extends Sorter {
         int h = endOffsets[i];
         final int bucketLen = h - prev;
         if (bucketLen > 1) {
-          sort(from + prev, from + h, k + 1);
+          sort(from + prev, from + h, k + 1, l + 1);
         }
         prev = h;
       }
     }
   }
 
+  // only used from assert
+  private boolean assertHistogram(int commonPrefixLength, int[] histogram) {
+    int numberOfUniqueBytes = 0;
+    for (int freq : histogram) {
+      if (freq > 0) {
+        numberOfUniqueBytes++;
+      }
+    }
+    if (numberOfUniqueBytes == 1) {
+      assert commonPrefixLength >= 1;
+    } else {
+      assert commonPrefixLength == 0 : commonPrefixLength;
+    }
+    return true;
+  }
+
   /** Return a number for the k-th character between 0 and {@link #HISTOGRAM_SIZE}. */
   private int getBucket(int i, int k) {
     return byteAt(i, k) + 1;
   }
 
-  /** Build a histogram of the number of values per {@link #getBucket(int, int) bucket}. */
-  private int[] buildHistogram(int from, int to, int k, int[] histogram) {
+  /** Build a histogram of the number of values per {@link #getBucket(int, int) bucket}
+   *  and return a common prefix length for all visited values.
+   *  @see #buildHistogram */
+  private int computeCommonPrefixLengthAndBuildHistogram(int from, int to, int k, int[] histogram) {
+    final int[] commonPrefix = this.commonPrefix;
+    int commonPrefixLength = Math.min(commonPrefix.length, maxLength - k);
+    for (int j = 0; j < commonPrefixLength; ++j) {
+      final int b = byteAt(from, k + j);
+      commonPrefix[j] = b;
+      if (b == -1) {
+        commonPrefixLength = j + 1;
+        break;
+      }
+    }
+
+    int i;
+    outer: for (i = from + 1; i < to; ++i) {
+      for (int j = 0; j < commonPrefixLength; ++j) {
+        final int b = byteAt(i, k + j);
+        if (b != commonPrefix[j]) {
+          commonPrefixLength = j;
+          if (commonPrefixLength == 0) { // we have no common prefix
+            histogram[commonPrefix[0] + 1] = i - from;
+            histogram[b + 1] = 1;
+            break outer;
+          }
+          break;
+        }
+      }
+    }
+
+    if (i < to) {
+      // the loop got broken because there is no common prefix
+      assert commonPrefixLength == 0;
+      buildHistogram(i + 1, to, k, histogram);
+    } else {
+      assert commonPrefixLength > 0;
+      histogram[commonPrefix[0] + 1] = to - from;
+    }
+
+    return commonPrefixLength;
+  }
+
+  /** Build an histogram of the k-th characters of values occurring between
+   *  offsets {@code from} and {@code to}, using {@link #getBucket}. */
+  private void buildHistogram(int from, int to, int k, int[] histogram) {
     for (int i = from; i < to; ++i) {
       histogram[getBucket(i, k)]++;
     }
-    return histogram;
   }
 
   /** Accumulate values of the histogram so that it does not store counts but

lucene/core/src/java/org/apache/lucene/util/RadixSelector.java

@@ -0,0 +1,278 @@
+/*
+ * 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.util;
+
+import java.util.Arrays;
+
+/** Radix selector.
+ *  <p>This implementation works similarly to a MSB radix sort except that it
+ *  only recurses into the sub partition that contains the desired value.
+ *  @lucene.internal */
+public abstract class RadixSelector extends Selector {
+
+  // after that many levels of recursion we fall back to introselect anyway
+  // this is used as a protection against the fact that radix sort performs
+  // worse when there are long common prefixes (probably because of cache
+  // locality)
+  private static final int LEVEL_THRESHOLD = 8;
+  // size of histograms: 256 + 1 to indicate that the string is finished
+  private static final int HISTOGRAM_SIZE = 257;
+  // buckets below this size will be sorted with introselect
+  private static final int LENGTH_THRESHOLD = 100;
+
+  // we store one histogram per recursion level
+  private final int[] histogram = new int[HISTOGRAM_SIZE];
+  private final int[] commonPrefix;
+
+  private final int maxLength;
+
+  /**
+   * Sole constructor.
+   * @param maxLength the maximum length of keys, pass {@link Integer#MAX_VALUE} if unknown.
+   */
+  protected RadixSelector(int maxLength) {
+    this.maxLength = maxLength;
+    this.commonPrefix = new int[Math.min(24, maxLength)];
+  }
+
+  /** Return the k-th byte of the entry at index {@code i}, or {@code -1} if
+   * its length is less than or equal to {@code k}. This may only be called
+   * with a value of {@code i} between {@code 0} included and
+   * {@code maxLength} excluded. */
+  protected abstract int byteAt(int i, int k);
+
+  /** Get a fall-back selector which may assume that the first {@code d} bytes
+   *  of all compared strings are equal. This fallback selector is used when
+   *  the range becomes narrow or when the maximum level of recursion has
+   *  been exceeded. */
+  protected Selector getFallbackSelector(int d) {
+    return new IntroSelector() {
+      @Override
+      protected void swap(int i, int j) {
+        RadixSelector.this.swap(i, j);
+      }
+
+      @Override
+      protected int compare(int i, int j) {
+        for (int o = d; o < maxLength; ++o) {
+          final int b1 = byteAt(i, o);
+          final int b2 = byteAt(j, o);
+          if (b1 != b2) {
+            return b1 - b2;
+          } else if (b1 == -1) {
+            break;
+          }
+        }
+        return 0;
+      }
+
+      @Override
+      protected void setPivot(int i) {
+        pivot.setLength(0);
+        for (int o = d; o < maxLength; ++o) {
+          final int b = byteAt(i, o);
+          if (b == -1) {
+            break;
+          }
+          pivot.append((byte) b);
+        }
+      }
+
+      @Override
+      protected int comparePivot(int j) {
+        for (int o = 0; o < pivot.length(); ++o) {
+          final int b1 = pivot.byteAt(o) & 0xff;
+          final int b2 = byteAt(j, d + o);
+          if (b1 != b2) {
+            return b1 - b2;
+          }
+        }
+        if (d + pivot.length() == maxLength) {
+          return 0;
+        }
+        return -1 - byteAt(j, d + pivot.length());
+      }
+
+      private final BytesRefBuilder pivot = new BytesRefBuilder();
+    };
+  }
+
+  @Override
+  public void select(int from, int to, int k) {
+    checkArgs(from, to, k);
+    select(from, to, k, 0, 0);
+  }
+
+  private void select(int from, int to, int k, int d, int l) {
+    if (to - from <= LENGTH_THRESHOLD || d >= LEVEL_THRESHOLD) {
+      getFallbackSelector(d).select(from, to, k);
+    } else {
+      radixSelect(from, to, k, d, l);
+    }
+  }
+
+  /**
+   * @param d the character number to compare
+   * @param l the level of recursion
+   */
+  private void radixSelect(int from, int to, int k, int d, int l) {
+    final int[] histogram = this.histogram;
+    Arrays.fill(histogram, 0);
+
+    final int commonPrefixLength = computeCommonPrefixLengthAndBuildHistogram(from, to, d, histogram);
+    if (commonPrefixLength > 0) {
+      // if there are no more chars to compare or if all entries fell into the
+      // first bucket (which means strings are shorter than d) then we are done
+      // otherwise recurse
+      if (d + commonPrefixLength < maxLength
+          && histogram[0] < to - from) {
+        radixSelect(from, to, k, d + commonPrefixLength, l);
+      }
+      return;
+    }
+    assert assertHistogram(commonPrefixLength, histogram);
+
+    int bucketFrom = from;
+    for (int bucket = 0; bucket < HISTOGRAM_SIZE; ++bucket) {
+      final int bucketTo = bucketFrom + histogram[bucket];
+
+      if (bucketTo > k) {
+        partition(from, to, bucket, bucketFrom, bucketTo, d);
+
+        if (bucket != 0 && d + 1 < maxLength) {
+          // all elements in bucket 0 are equal so we only need to recurse if bucket != 0
+          select(bucketFrom, bucketTo, k, d + 1, l + 1);
+        }
+        return;
+      }
+      bucketFrom = bucketTo;
+    }
+    throw new AssertionError("Unreachable code");
+  }
+
+  // only used from assert
+  private boolean assertHistogram(int commonPrefixLength, int[] histogram) {
+    int numberOfUniqueBytes = 0;
+    for (int freq : histogram) {
+      if (freq > 0) {
+        numberOfUniqueBytes++;
+      }
+    }
+    if (numberOfUniqueBytes == 1) {
+      assert commonPrefixLength >= 1;
+    } else {
+      assert commonPrefixLength == 0;
+    }
+    return true;
+  }
+
+  /** Return a number for the k-th character between 0 and {@link #HISTOGRAM_SIZE}. */
+  private int getBucket(int i, int k) {
+    return byteAt(i, k) + 1;
+  }
+
+  /** Build a histogram of the number of values per {@link #getBucket(int, int) bucket}
+   *  and return a common prefix length for all visited values.
+   *  @see #buildHistogram */
+  private int computeCommonPrefixLengthAndBuildHistogram(int from, int to, int k, int[] histogram) {
+    final int[] commonPrefix = this.commonPrefix;
+    int commonPrefixLength = Math.min(commonPrefix.length, maxLength - k);
+    for (int j = 0; j < commonPrefixLength; ++j) {
+      final int b = byteAt(from, k + j);
+      commonPrefix[j] = b;
+      if (b == -1) {
+        commonPrefixLength = j + 1;
+        break;
+      }
+    }
+
+    int i;
+    outer: for (i = from + 1; i < to; ++i) {
+      for (int j = 0; j < commonPrefixLength; ++j) {
+        final int b = byteAt(i, k + j);
+        if (b != commonPrefix[j]) {
+          commonPrefixLength = j;
+          if (commonPrefixLength == 0) { // we have no common prefix
+            histogram[commonPrefix[0] + 1] = i - from;
+            histogram[b + 1] = 1;
+            break outer;
+          }
+          break;
+        }
+      }
+    }
+
+    if (i < to) {
+      // the loop got broken because there is no common prefix
+      assert commonPrefixLength == 0;
+      buildHistogram(i + 1, to, k, histogram);
+    } else {
+      assert commonPrefixLength > 0;
+      histogram[commonPrefix[0] + 1] = to - from;
+    }
+
+    return commonPrefixLength;
+  }
+
+  /** Build an histogram of the k-th characters of values occurring between
+   *  offsets {@code from} and {@code to}, using {@link #getBucket}. */
+  private void buildHistogram(int from, int to, int k, int[] histogram) {
+    for (int i = from; i < to; ++i) {
+      histogram[getBucket(i, k)]++;
+    }
+  }
+
+  /** Reorder elements so that all of them that fall into {@code bucket} are
+   *  between offsets {@code bucketFrom} and {@code bucketTo}. */
+  private void partition(int from, int to, int bucket, int bucketFrom, int bucketTo, int d) {
+    int left = from;
+    int right = to - 1;
+
+    int slot = bucketFrom;
+
+    for (;;) {
+      int leftBucket = getBucket(left, d);
+      int rightBucket = getBucket(right, d);
+
+      while (leftBucket <= bucket && left < bucketFrom) {
+        if (leftBucket == bucket) {
+          swap(left, slot++);
+        } else {
+          ++left;
+        }
+        leftBucket = getBucket(left, d);
+      }
+
+      while (rightBucket >= bucket && right >= bucketTo) {
+        if (rightBucket == bucket) {
+          swap(right, slot++);
+        } else {
+          --right;
+        }
+        rightBucket = getBucket(right, d);
+      }
+
+      if (left < bucketFrom && right >= bucketTo) {
+        swap(left++, right--);
+      } else {
+        assert left == bucketFrom;
+        assert right == bucketTo - 1;
+        break;
+      }
+    }
+  }
+}

lucene/core/src/java/org/apache/lucene/util/Selector.java

@@ -0,0 +1,41 @@
+/*
+ * 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.util;
+
+/** An implementation of a selection algorithm, ie. computing the k-th greatest
+ *  value from a collection. */
+public abstract class Selector {
+
+  /** Reorder elements so that the element at position {@code k} is the same
+   *  as if all elements were sorted and all other elements are partitioned
+   *  around it: {@code [from, k)} only contains elements that are less than
+   *  or equal to {@code k} and {@code (k, to)} only contains elements that
+   *  are greater than or equal to {@code k}. */
+  public abstract void select(int from, int to, int k);
+
+  void checkArgs(int from, int to, int k) {
+    if (k < from) {
+      throw new IllegalArgumentException("k must be >= from");
+    }
+    if (k >= to) {
+      throw new IllegalArgumentException("k must be < to");
+    }
+  }
+
+  /** Swap values at slots <code>i</code> and <code>j</code>. */
+  protected abstract void swap(int i, int j);
+}

lucene/core/src/java/org/apache/lucene/util/Sorter.java

@@ -23,7 +23,7 @@ import java.util.Comparator;
  * @lucene.internal */
 public abstract class Sorter {
 
-  static final int INSERTION_SORT_THRESHOLD = 20;
+  static final int BINARY_SORT_THRESHOLD = 20;
 
   /** Sole constructor, used for inheritance. */
   protected Sorter() {}
@@ -36,6 +36,20 @@ public abstract class Sorter {
   /** Swap values at slots <code>i</code> and <code>j</code>. */
   protected abstract void swap(int i, int j);
 
+  private int pivotIndex;
+
+  /** Save the value at slot <code>i</code> so that it can later be used as a
+   * pivot, see {@link #comparePivot(int)}. */
+  protected void setPivot(int i) {
+    pivotIndex = i;
+  }
+
+  /** Compare the pivot with the slot at <code>j</code>, similarly to
+   *  {@link #compare(int, int) compare(i, j)}. */
+  protected int comparePivot(int j) {
+    return compare(pivotIndex, j);
+  }
+
   /** Sort the slice which starts at <code>from</code> (inclusive) and ends at
    *  <code>to</code> (exclusive). */
   public abstract void sort(int from, int to);
@@ -163,54 +177,41 @@ public abstract class Sorter {
     }
   }
 
-  void insertionSort(int from, int to) {
-    for (int i = from + 1; i < to; ++i) {
-      for (int j = i; j > from; --j) {
-        if (compare(j - 1, j) > 0) {
-          swap(j - 1, j);
-        } else {
-          break;
-        }
-      }
-    }
-  }
-
+  /**
+   * A binary sort implementation. This performs {@code O(n*log(n))} comparisons
+   * and {@code O(n^2)} swaps. It is typically used by more sophisticated
+   * implementations as a fall-back when the numbers of items to sort has become
+   * less than {@value #BINARY_SORT_THRESHOLD}.
+   */
   void binarySort(int from, int to) {
     binarySort(from, to, from + 1);
   }
 
   void binarySort(int from, int to, int i) {
     for ( ; i < to; ++i) {
+      setPivot(i);
       int l = from;
       int h = i - 1;
       while (l <= h) {
         final int mid = (l + h) >>> 1;
-        final int cmp = compare(i, mid);
+        final int cmp = comparePivot(mid);
         if (cmp < 0) {
           h = mid - 1;
         } else {
           l = mid + 1;
         }
       }
-      switch (i - l) {
-      case 2:
-        swap(l + 1, l + 2);
-        swap(l, l + 1);
-        break;
-      case 1:
-        swap(l, l + 1);
-        break;
-      case 0:
-        break;
-      default:
       for (int j = i; j > l; --j) {
         swap(j - 1, j);
       }
-        break;
-      }
     }
   }
 
+  /**
+   * Use heap sort to sort items between {@code from} inclusive and {@code to}
+   * exclusive. This runs in {@code O(n*log(n))} and is used as a fall-back by
+   * {@link IntroSorter}.
+   */
   void heapSort(int from, int to) {
     if (to - from <= 1) {
       return;

lucene/core/src/java/org/apache/lucene/util/automaton/Automaton.java

@@ -357,13 +357,13 @@ public class Automaton implements Accountable {
   }
 
   private void growStates() {
-    if (nextState+2 >= states.length) {
+    if (nextState+2 > states.length) {
       states = ArrayUtil.grow(states, nextState+2);
     }
   }
 
   private void growTransitions() {
-    if (nextTransition+3 >= transitions.length) {
+    if (nextTransition+3 > transitions.length) {
       transitions = ArrayUtil.grow(transitions, nextTransition+3);
     }
   }

lucene/core/src/java/org/apache/lucene/util/bkd/BKDWriter.java

@@ -25,6 +25,7 @@ import java.util.List;
 import java.util.function.IntFunction;
 
 import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.MutablePointsReader;
 import org.apache.lucene.index.MergeState;
 import org.apache.lucene.index.PointValues.IntersectVisitor;
 import org.apache.lucene.index.PointValues.Relation;
@@ -111,7 +112,8 @@ public class BKDWriter implements Closeable {
   final byte[] scratchDiff;
   final byte[] scratch1;
   final byte[] scratch2;
-  final BytesRef scratchBytesRef = new BytesRef();
+  final BytesRef scratchBytesRef1 = new BytesRef();
+  final BytesRef scratchBytesRef2 = new BytesRef();
   final int[] commonPrefixLengths;
 
   protected final FixedBitSet docsSeen;
@@ -173,7 +175,6 @@ public class BKDWriter implements Closeable {
     packedBytesLength = numDims * bytesPerDim;
 
     scratchDiff = new byte[bytesPerDim];
-    scratchBytesRef.length = packedBytesLength;
     scratch1 = new byte[packedBytesLength];
     scratch2 = new byte[packedBytesLength];
     commonPrefixLengths = new int[numDims];
@@ -204,7 +205,7 @@ public class BKDWriter implements Closeable {
     // all recursive halves (i.e. 16 + 8 + 4 + 2) so the memory usage is 2X
     // what that level would consume, so we multiply by 0.5 to convert from
     // bytes to points here.  Each dimension has its own sorted partition, so
-    // we must divide by numDims as well.
+    // we must divide by numDims as wel.
 
     maxPointsSortInHeap = (int) (0.5 * (maxMBSortInHeap * 1024 * 1024) / (bytesPerDoc * numDims));
 
@@ -416,15 +417,25 @@ public class BKDWriter implements Closeable {
     }
   }
 
-  /** More efficient bulk-add for incoming {@link BKDReader}s.  This does a merge sort of the already
-   *  sorted values and currently only works when numDims==1.  This returns -1 if all documents containing
-   *  dimensional values were deleted. */
-  public long merge(IndexOutput out, List<MergeState.DocMap> docMaps, List<BKDReader> readers) throws IOException {
-    if (numDims != 1) {
-      throw new UnsupportedOperationException("numDims must be 1 but got " + numDims);
+  /** Write a field from a {@link MutablePointsReader}. This way of writing
+   *  points is faster than regular writes with {@link BKDWriter#add} since
+   *  there is opportunity for reordering points before writing them to
+   *  disk. This method does not use transient disk in order to reorder points.
+   */
+  public long writeField(IndexOutput out, String fieldName, MutablePointsReader reader) throws IOException {
+    if (numDims == 1) {
+      return writeField1Dim(out, fieldName, reader);
+    } else {
+      return writeFieldNDims(out, fieldName, reader);
     }
+  }
+
+
+  /* In the 2+D case, we recursively pick the split dimension, compute the
+   * median value and partition other values around it. */
+  private long writeFieldNDims(IndexOutput out, String fieldName, MutablePointsReader reader) throws IOException {
     if (pointCount != 0) {
-      throw new IllegalStateException("cannot mix add and merge");
+      throw new IllegalStateException("cannot mix add and writeField");
     }
 
     // Catch user silliness:
@@ -435,6 +446,81 @@ public class BKDWriter implements Closeable {
     // Mark that we already finished:
     heapPointWriter = null;
 
+    long countPerLeaf = pointCount = reader.size(fieldName);
+    long innerNodeCount = 1;
+
+    while (countPerLeaf > maxPointsInLeafNode) {
+      countPerLeaf = (countPerLeaf+1)/2;
+      innerNodeCount *= 2;
+    }
+
+    int numLeaves = Math.toIntExact(innerNodeCount);
+
+    checkMaxLeafNodeCount(numLeaves);
+
+    final byte[] splitPackedValues = new byte[numLeaves * (bytesPerDim + 1)];
+    final long[] leafBlockFPs = new long[numLeaves];
+
+    // compute the min/max for this slice
+    Arrays.fill(minPackedValue, (byte) 0xff);
+    Arrays.fill(maxPackedValue, (byte) 0);
+    for (int i = 0; i < Math.toIntExact(pointCount); ++i) {
+      reader.getValue(i, scratchBytesRef1);
+      for(int dim=0;dim<numDims;dim++) {
+        int offset = dim*bytesPerDim;
+        if (StringHelper.compare(bytesPerDim, scratchBytesRef1.bytes, scratchBytesRef1.offset + offset, minPackedValue, offset) < 0) {
+          System.arraycopy(scratchBytesRef1.bytes, scratchBytesRef1.offset + offset, minPackedValue, offset, bytesPerDim);
+        }
+        if (StringHelper.compare(bytesPerDim, scratchBytesRef1.bytes, scratchBytesRef1.offset + offset, maxPackedValue, offset) > 0) {
+          System.arraycopy(scratchBytesRef1.bytes, scratchBytesRef1.offset + offset, maxPackedValue, offset, bytesPerDim);
+        }
+      }
+
+      docsSeen.set(reader.getDocID(i));
+    }
+
+    build(1, numLeaves, reader, 0, Math.toIntExact(pointCount), out,
+        minPackedValue, maxPackedValue, splitPackedValues, leafBlockFPs,
+        new int[maxPointsInLeafNode]);
+
+    long indexFP = out.getFilePointer();
+    writeIndex(out, leafBlockFPs, splitPackedValues);
+    return indexFP;
+  }
+
+
+  /* In the 1D case, we can simply sort points in ascending order and use the
+   * same writing logic as we use at merge time. */
+  private long writeField1Dim(IndexOutput out, String fieldName, MutablePointsReader reader) throws IOException {
+    MutablePointsReaderUtils.sort(maxDoc, packedBytesLength, reader, 0, Math.toIntExact(reader.size(fieldName)));
+
+    final OneDimensionBKDWriter oneDimWriter = new OneDimensionBKDWriter(out);
+
+    reader.intersect(fieldName, new IntersectVisitor() {
+
+      @Override
+      public void visit(int docID, byte[] packedValue) throws IOException {
+        oneDimWriter.add(packedValue, docID);
+      }
+
+      @Override
+      public void visit(int docID) throws IOException {
+        throw new IllegalStateException();
+      }
+
+      @Override
+      public Relation compare(byte[] minPackedValue, byte[] maxPackedValue) {
+        return Relation.CELL_CROSSES_QUERY;
+      }
+    });
+
+    return oneDimWriter.finish();
+  }
+
+  /** More efficient bulk-add for incoming {@link BKDReader}s.  This does a merge sort of the already
+   *  sorted values and currently only works when numDims==1.  This returns -1 if all documents containing
+   *  dimensional values were deleted. */
+  public long merge(IndexOutput out, List<MergeState.DocMap> docMaps, List<BKDReader> readers) throws IOException {
     assert docMaps == null || readers.size() == docMaps.size();
 
     BKDMergeQueue queue = new BKDMergeQueue(bytesPerDim, readers.size());
@@ -453,72 +539,14 @@ public class BKDWriter implements Closeable {
       }
     }
 
-    if (queue.size() == 0) {
-      return -1;
-    }
-
-    int leafCount = 0;
-    List<Long> leafBlockFPs = new ArrayList<>();
-    List<byte[]> leafBlockStartValues = new ArrayList<>();
-
-    // Target halfway between min and max allowed for the leaf:
-    int pointsPerLeafBlock = (int) (0.75 * maxPointsInLeafNode);
-    //System.out.println("POINTS PER: " + pointsPerLeafBlock);
-
-    byte[] lastPackedValue = new byte[bytesPerDim];
-    byte[] firstPackedValue = new byte[bytesPerDim];
-    long valueCount = 0;
-
-    // Buffer up each leaf block's docs and values
-    int[] leafBlockDocIDs = new int[maxPointsInLeafNode];
-    byte[][] leafBlockPackedValues = new byte[maxPointsInLeafNode][];
-    for(int i=0;i<maxPointsInLeafNode;i++) {
-      leafBlockPackedValues[i] = new byte[packedBytesLength];
-    }
-    Arrays.fill(commonPrefixLengths, bytesPerDim);
+    OneDimensionBKDWriter oneDimWriter = new OneDimensionBKDWriter(out);
 
     while (queue.size() != 0) {
       MergeReader reader = queue.top();
       // System.out.println("iter reader=" + reader);
 
       // NOTE: doesn't work with subclasses (e.g. SimpleText!)
-      int docID = reader.docID;
-      leafBlockDocIDs[leafCount] = docID;
-      System.arraycopy(reader.state.scratchPackedValue, 0, leafBlockPackedValues[leafCount], 0, packedBytesLength);
-      docsSeen.set(docID);
-
-      if (valueCount == 0) {
-        System.arraycopy(reader.state.scratchPackedValue, 0, minPackedValue, 0, packedBytesLength);
-      }
-      System.arraycopy(reader.state.scratchPackedValue, 0, maxPackedValue, 0, packedBytesLength);
-
-      assert numDims > 1 || valueInOrder(valueCount, lastPackedValue, reader.state.scratchPackedValue, 0);
-      valueCount++;
-      if (pointCount > totalPointCount) {
-        throw new IllegalStateException("totalPointCount=" + totalPointCount + " was passed when we were created, but we just hit " + pointCount + " values");
-      }
-
-      if (leafCount == 0) {
-        if (leafBlockFPs.size() > 0) {
-          // Save the first (minimum) value in each leaf block except the first, to build the split value index in the end:
-          leafBlockStartValues.add(Arrays.copyOf(reader.state.scratchPackedValue, bytesPerDim));
-        }
-        Arrays.fill(commonPrefixLengths, bytesPerDim);
-        System.arraycopy(reader.state.scratchPackedValue, 0, firstPackedValue, 0, bytesPerDim);
-      } else {
-        // Find per-dim common prefix:
-        for(int dim=0;dim<numDims;dim++) {
-          int offset = dim * bytesPerDim;
-          for(int j=0;j<commonPrefixLengths[dim];j++) {
-            if (firstPackedValue[offset+j] != reader.state.scratchPackedValue[offset+j]) {
-              commonPrefixLengths[dim] = j;
-              break;
-            }
-          }
-        }
-      }
-
-      leafCount++;
+      oneDimWriter.add(reader.state.scratchPackedValue, reader.docID);
 
       if (reader.next()) {
         queue.updateTop();
@@ -526,35 +554,78 @@ public class BKDWriter implements Closeable {
         // This segment was exhausted
         queue.pop();
       }
+    }
 
+    return oneDimWriter.finish();
+  }
+
+  private class OneDimensionBKDWriter {
+
+    final IndexOutput out;
+    final List<Long> leafBlockFPs = new ArrayList<>();
+    final List<byte[]> leafBlockStartValues = new ArrayList<>();
+    final byte[] leafValues = new byte[maxPointsInLeafNode * packedBytesLength];
+    final int[] leafDocs = new int[maxPointsInLeafNode];
+    long valueCount;
+    int leafCount;
+
+    OneDimensionBKDWriter(IndexOutput out) {
+      if (numDims != 1) {
+        throw new UnsupportedOperationException("numDims must be 1 but got " + numDims);
+      }
+      if (pointCount != 0) {
+        throw new IllegalStateException("cannot mix add and merge");
+      }
+
+      // Catch user silliness:
+      if (heapPointWriter == null && tempInput == null) {
+        throw new IllegalStateException("already finished");
+      }
+
+      // Mark that we already finished:
+      heapPointWriter = null;
+
+      this.out = out;
+
+      lastPackedValue = new byte[packedBytesLength];
+    }
+
+    // for asserts
+    final byte[] lastPackedValue;
+    int lastDocID;
+
+    void add(byte[] packedValue, int docID) throws IOException {
+      assert valueInOrder(valueCount + leafCount,
+          0, lastPackedValue, packedValue, 0, docID, lastDocID);
+
+      System.arraycopy(packedValue, 0, leafValues, leafCount * packedBytesLength, packedBytesLength);
+      leafDocs[leafCount] = docID;
+      docsSeen.set(docID);
+      leafCount++;
+
+      if (valueCount > totalPointCount) {
+        throw new IllegalStateException("totalPointCount=" + totalPointCount + " was passed when we were created, but we just hit " + pointCount + " values");
+      }
+
+      if (leafCount == maxPointsInLeafNode) {
         // We write a block once we hit exactly the max count ... this is different from
         // when we flush a new segment, where we write between max/2 and max per leaf block,
         // so merged segments will behave differently from newly flushed segments:
-      if (leafCount == pointsPerLeafBlock || queue.size() == 0) {
-        leafBlockFPs.add(out.getFilePointer());
-        checkMaxLeafNodeCount(leafBlockFPs.size());
-
-        writeLeafBlockDocs(out, leafBlockDocIDs, 0, leafCount);
-        writeCommonPrefixes(out, commonPrefixLengths, firstPackedValue);
-
-        final IntFunction<BytesRef> packedValues = new IntFunction<BytesRef>() {
-          final BytesRef scratch = new BytesRef();
-
-          {
-            scratch.length = packedBytesLength;
-            scratch.offset = 0;
-          }
-
-          @Override
-          public BytesRef apply(int i) {
-            scratch.bytes = leafBlockPackedValues[i];
-            return scratch;
-          }
-        };
-        writeLeafBlockPackedValues(out, commonPrefixLengths, leafCount, 0, packedValues);
-
+        writeLeafBlock();
         leafCount = 0;
       }
+
+      assert (lastDocID = docID) >= 0; // only assign when asserts are enabled
+    }
+
+    public long finish() throws IOException {
+      if (leafCount > 0) {
+        writeLeafBlock();
+        leafCount = 0;
+      }
+
+      if (valueCount == 0) {
+        return -1;
       }
 
       pointCount = valueCount;
@@ -575,6 +646,60 @@ public class BKDWriter implements Closeable {
       return indexFP;
     }
 
+    private void writeLeafBlock() throws IOException {
+      assert leafCount != 0;
+      if (valueCount == 0) {
+        System.arraycopy(leafValues, 0, minPackedValue, 0, packedBytesLength);
+      }
+      System.arraycopy(leafValues, (leafCount - 1) * packedBytesLength, maxPackedValue, 0, packedBytesLength);
+
+      valueCount += leafCount;
+
+      if (leafBlockFPs.size() > 0) {
+        // Save the first (minimum) value in each leaf block except the first, to build the split value index in the end:
+        leafBlockStartValues.add(Arrays.copyOf(leafValues, packedBytesLength));
+      }
+      leafBlockFPs.add(out.getFilePointer());
+      checkMaxLeafNodeCount(leafBlockFPs.size());
+
+      Arrays.fill(commonPrefixLengths, bytesPerDim);
+      // Find per-dim common prefix:
+      for(int dim=0;dim<numDims;dim++) {
+        int offset1 = dim * bytesPerDim;
+        int offset2 = (leafCount - 1) * packedBytesLength + offset1;
+        for(int j=0;j<commonPrefixLengths[dim];j++) {
+          if (leafValues[offset1+j] != leafValues[offset2+j]) {
+            commonPrefixLengths[dim] = j;
+            break;
+          }
+        }
+      }
+
+      writeLeafBlockDocs(out, leafDocs, 0, leafCount);
+      writeCommonPrefixes(out, commonPrefixLengths, leafValues);
+
+      final IntFunction<BytesRef> packedValues = new IntFunction<BytesRef>() {
+        final BytesRef scratch = new BytesRef();
+
+        {
+          scratch.length = packedBytesLength;
+          scratch.bytes = leafValues;
+        }
+
+        @Override
+        public BytesRef apply(int i) {
+          scratch.offset = packedBytesLength * i;
+          return scratch;
+        }
+      };
+      assert valuesInOrderAndBounds(leafCount, 0, Arrays.copyOf(leafValues, packedBytesLength),
+          Arrays.copyOfRange(leafValues, (leafCount - 1) * packedBytesLength, leafCount * packedBytesLength),
+          packedValues, leafDocs, 0);
+      writeLeafBlockPackedValues(out, commonPrefixLengths, leafCount, 0, packedValues);
+    }
+
+  }
+
   // TODO: there must be a simpler way?
   private void rotateToTree(int nodeID, int offset, int count, byte[] index, List<byte[]> leafBlockStartValues) {
     //System.out.println("ROTATE: nodeID=" + nodeID + " offset=" + offset + " count=" + count + " bpd=" + bytesPerDim + " index.length=" + index.length);
@@ -686,6 +811,7 @@ public class BKDWriter implements Closeable {
   }
 
   private PointWriter sort(int dim) throws IOException {
+    assert dim >= 0 && dim < numDims;
 
     if (heapPointWriter != null) {
 
@@ -1110,6 +1236,132 @@ public class BKDWriter implements Closeable {
     }
   }
 
+  /* Recursively reorders the provided reader and writes the bkd-tree on the fly. */
+  private void build(int nodeID, int leafNodeOffset,
+      MutablePointsReader reader, int from, int to,
+      IndexOutput out,
+      byte[] minPackedValue, byte[] maxPackedValue,
+      byte[] splitPackedValues,
+      long[] leafBlockFPs,
+      int[] spareDocIds) throws IOException {
+
+    if (nodeID >= leafNodeOffset) {
+      // leaf node
+      final int count = to - from;
+      assert count <= maxPointsInLeafNode;
+
+      // Compute common prefixes
+      Arrays.fill(commonPrefixLengths, bytesPerDim);
+      reader.getValue(from, scratchBytesRef1);
+      for (int i = from + 1; i < to; ++i) {
+        reader.getValue(i, scratchBytesRef2);
+        for (int dim=0;dim<numDims;dim++) {
+          final int offset = dim * bytesPerDim;
+          for(int j=0;j<commonPrefixLengths[dim];j++) {
+            if (scratchBytesRef1.bytes[scratchBytesRef1.offset+offset+j] != scratchBytesRef2.bytes[scratchBytesRef2.offset+offset+j]) {
+              commonPrefixLengths[dim] = j;
+              break;
+            }
+          }
+        }
+      }
+
+      // Find the dimension that has the least number of unique bytes at commonPrefixLengths[dim]
+      FixedBitSet[] usedBytes = new FixedBitSet[numDims];
+      for (int dim = 0; dim < numDims; ++dim) {
+        if (commonPrefixLengths[dim] < bytesPerDim) {
+          usedBytes[dim] = new FixedBitSet(256);
+        }
+      }
+      for (int i = from + 1; i < to; ++i) {
+        for (int dim=0;dim<numDims;dim++) {
+          if (usedBytes[dim] != null) {
+            byte b = reader.getByteAt(i, dim * bytesPerDim + commonPrefixLengths[dim]);
+            usedBytes[dim].set(Byte.toUnsignedInt(b));
+          }
+        }
+      }
+      int sortedDim = 0;
+      int sortedDimCardinality = Integer.MAX_VALUE;
+      for (int dim = 0; dim < numDims; ++dim) {
+        if (usedBytes[dim] != null) {
+          final int cardinality = usedBytes[dim].cardinality();
+          if (cardinality < sortedDimCardinality) {
+            sortedDim = dim;
+            sortedDimCardinality = cardinality;
+          }
+        }
+      }
+
+      // sort by sortedDim
+      MutablePointsReaderUtils.sortByDim(sortedDim, bytesPerDim, commonPrefixLengths,
+          reader, from, to, scratchBytesRef1, scratchBytesRef2);
+
+      // Save the block file pointer:
+      leafBlockFPs[nodeID - leafNodeOffset] = out.getFilePointer();
+
+      // Write doc IDs
+      int[] docIDs = spareDocIds;
+      for (int i = from; i < to; ++i) {
+        docIDs[i - from] = reader.getDocID(i);
+      }
+      writeLeafBlockDocs(out, docIDs, 0, count);
+
+      // Write the common prefixes:
+      reader.getValue(from, scratchBytesRef1);
+      System.arraycopy(scratchBytesRef1.bytes, scratchBytesRef1.offset, scratch1, 0, packedBytesLength);
+      writeCommonPrefixes(out, commonPrefixLengths, scratch1);
+
+      // Write the full values:
+      IntFunction<BytesRef> packedValues = new IntFunction<BytesRef>() {
+        @Override
+        public BytesRef apply(int i) {
+          reader.getValue(from + i, scratchBytesRef1);
+          return scratchBytesRef1;
+        }
+      };
+      assert valuesInOrderAndBounds(count, sortedDim, minPackedValue, maxPackedValue, packedValues,
+          docIDs, 0);
+      writeLeafBlockPackedValues(out, commonPrefixLengths, count, sortedDim, packedValues);
+
+    } else {
+      // inner node
+
+      // compute the split dimension and partition around it
+      final int splitDim = split(minPackedValue, maxPackedValue);
+      final int mid = (from + to + 1) >>> 1;
+
+      int commonPrefixLen = bytesPerDim;
+      for (int i = 0; i < bytesPerDim; ++i) {
+        if (minPackedValue[splitDim * bytesPerDim + i] != maxPackedValue[splitDim * bytesPerDim + i]) {
+          commonPrefixLen = i;
+          break;
+        }
+      }
+      MutablePointsReaderUtils.partition(maxDoc, splitDim, bytesPerDim, commonPrefixLen,
+          reader, from, to, mid, scratchBytesRef1, scratchBytesRef2);
+
+      // set the split value
+      final int address = nodeID * (1+bytesPerDim);
+      splitPackedValues[address] = (byte) splitDim;
+      reader.getValue(mid, scratchBytesRef1);
+      System.arraycopy(scratchBytesRef1.bytes, scratchBytesRef1.offset + splitDim * bytesPerDim, splitPackedValues, address + 1, bytesPerDim);
+
+      byte[] minSplitPackedValue = Arrays.copyOf(minPackedValue, packedBytesLength);
+      byte[] maxSplitPackedValue = Arrays.copyOf(maxPackedValue, packedBytesLength);
+      System.arraycopy(scratchBytesRef1.bytes, scratchBytesRef1.offset + splitDim * bytesPerDim,
+          minSplitPackedValue, splitDim * bytesPerDim, bytesPerDim);
+      System.arraycopy(scratchBytesRef1.bytes, scratchBytesRef1.offset + splitDim * bytesPerDim,
+          maxSplitPackedValue, splitDim * bytesPerDim, bytesPerDim);
+
+      // recurse
+      build(nodeID * 2, leafNodeOffset, reader, from, mid, out,
+          minPackedValue, maxSplitPackedValue, splitPackedValues, leafBlockFPs, spareDocIds);
+      build(nodeID * 2 + 1, leafNodeOffset, reader, mid, to, out,
+          minSplitPackedValue, maxPackedValue, splitPackedValues, leafBlockFPs, spareDocIds);
+    }
+  }
+
   /** The array (sized numDims) of PathSlice describe the cell we have currently recursed to. */
   private void build(int nodeID, int leafNodeOffset,
                      PathSlice[] slices,
@@ -1217,7 +1469,8 @@ public class BKDWriter implements Closeable {
           return scratch;
         }
       };
-      assert valuesInOrderAndBounds(count, minPackedValue, maxPackedValue, packedValues);
+      assert valuesInOrderAndBounds(count, sortedDim, minPackedValue, maxPackedValue, packedValues,
+          heapSource.docIDs, Math.toIntExact(source.start));
       writeLeafBlockPackedValues(out, commonPrefixLengths, count, sortedDim, packedValues);
 
     } else {
@@ -1321,12 +1574,16 @@ public class BKDWriter implements Closeable {
   }
 
   // only called from assert
-  private boolean valuesInOrderAndBounds(int count, byte[] minPackedValue, byte[] maxPackedValue, IntFunction<BytesRef> values) throws IOException {
-    byte[] lastPackedValue = new byte[bytesPerDim];
+  private boolean valuesInOrderAndBounds(int count, int sortedDim, byte[] minPackedValue, byte[] maxPackedValue,
+      IntFunction<BytesRef> values, int[] docs, int docsOffset) throws IOException {
+    byte[] lastPackedValue = new byte[packedBytesLength];
+    int lastDoc = -1;
     for (int i=0;i<count;i++) {
       BytesRef packedValue = values.apply(i);
       assert packedValue.length == packedBytesLength;
-      assert numDims != 1 || valueInOrder(i, lastPackedValue, packedValue.bytes, packedValue.offset);
+      assert valueInOrder(i, sortedDim, lastPackedValue, packedValue.bytes, packedValue.offset,
+          docs[docsOffset + i], lastDoc);
+      lastDoc = docs[docsOffset + i];
 
       // Make sure this value does in fact fall within this leaf cell:
       assert valueInBounds(packedValue, minPackedValue, maxPackedValue);
@@ -1335,11 +1592,19 @@ public class BKDWriter implements Closeable {
   }
 
   // only called from assert
-  private boolean valueInOrder(long ord, byte[] lastPackedValue, byte[] packedValue, int packedValueOffset) {
-    if (ord > 0 && StringHelper.compare(bytesPerDim, lastPackedValue, 0, packedValue, packedValueOffset) > 0) {
+  private boolean valueInOrder(long ord, int sortedDim, byte[] lastPackedValue, byte[] packedValue, int packedValueOffset,
+      int doc, int lastDoc) {
+    int dimOffset = sortedDim * bytesPerDim;
+    if (ord > 0) {
+      int cmp = StringHelper.compare(bytesPerDim, lastPackedValue, dimOffset, packedValue, packedValueOffset + dimOffset);
+      if (cmp > 0) {
         throw new AssertionError("values out of order: last value=" + new BytesRef(lastPackedValue) + " current value=" + new BytesRef(packedValue, packedValueOffset, packedBytesLength) + " ord=" + ord);
       }
-    System.arraycopy(packedValue, packedValueOffset, lastPackedValue, 0, bytesPerDim);
+      if (cmp == 0 && doc < lastDoc) {
+        throw new AssertionError("docs out of order: last doc=" + lastDoc + " current doc=" + doc + " ord=" + ord);
+      }
+    }
+    System.arraycopy(packedValue, packedValueOffset, lastPackedValue, 0, packedBytesLength);
     return true;
   }
 

lucene/core/src/java/org/apache/lucene/util/bkd/MutablePointsReaderUtils.java

@@ -0,0 +1,186 @@
+/*
+ * 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.util.bkd;
+
+import org.apache.lucene.codecs.MutablePointsReader;
+import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.IntroSelector;
+import org.apache.lucene.util.IntroSorter;
+import org.apache.lucene.util.MSBRadixSorter;
+import org.apache.lucene.util.RadixSelector;
+import org.apache.lucene.util.Selector;
+import org.apache.lucene.util.StringHelper;
+import org.apache.lucene.util.packed.PackedInts;
+
+final class MutablePointsReaderUtils {
+
+  MutablePointsReaderUtils() {}
+
+  /** Sort the given {@link MutablePointsReader} based on its packed value then doc ID. */
+  static void sort(int maxDoc, int packedBytesLength,
+      MutablePointsReader reader, int from, int to) {
+    final int bitsPerDocId = PackedInts.bitsRequired(maxDoc - 1);
+    new MSBRadixSorter(packedBytesLength + (bitsPerDocId + 7) / 8) {
+
+      @Override
+      protected void swap(int i, int j) {
+        reader.swap(i, j);
+      }
+
+      @Override
+      protected int byteAt(int i, int k) {
+        if (k < packedBytesLength) {
+          return Byte.toUnsignedInt(reader.getByteAt(i, k));
+        } else {
+          final int shift = bitsPerDocId - ((k - packedBytesLength + 1) << 3);
+          return (reader.getDocID(i) >>> Math.max(0, shift)) & 0xff;
+        }
+      }
+
+      @Override
+      protected org.apache.lucene.util.Sorter getFallbackSorter(int k) {
+        return new IntroSorter() {
+
+          final BytesRef pivot = new BytesRef();
+          final BytesRef scratch = new BytesRef();
+          int pivotDoc;
+
+          @Override
+          protected void swap(int i, int j) {
+            reader.swap(i, j);
+          }
+
+          @Override
+          protected void setPivot(int i) {
+            reader.getValue(i, pivot);
+            pivotDoc = reader.getDocID(i);
+          }
+
+          @Override
+          protected int comparePivot(int j) {
+            if (k < packedBytesLength) {
+              reader.getValue(j, scratch);
+              int cmp = StringHelper.compare(packedBytesLength - k, pivot.bytes, pivot.offset + k, scratch.bytes, scratch.offset + k);
+              if (cmp != 0) {
+                return cmp;
+              }
+            }
+            return pivotDoc - reader.getDocID(j);
+          }
+        };
+      }
+
+    }.sort(from, to);
+  }
+
+  /** Sort points on the given dimension. */
+  static void sortByDim(int sortedDim, int bytesPerDim, int[] commonPrefixLengths,
+      MutablePointsReader reader, int from, int to,
+      BytesRef scratch1, BytesRef scratch2) {
+
+    // No need for a fancy radix sort here, this is called on the leaves only so
+    // there are not many values to sort
+    final int offset = sortedDim * bytesPerDim + commonPrefixLengths[sortedDim];
+    final int numBytesToCompare = bytesPerDim - commonPrefixLengths[sortedDim];
+    new IntroSorter() {
+
+      final BytesRef pivot = scratch1;
+      int pivotDoc = -1;
+
+      @Override
+      protected void swap(int i, int j) {
+        reader.swap(i, j);
+      }
+
+      @Override
+      protected void setPivot(int i) {
+        reader.getValue(i, pivot);
+        pivotDoc = reader.getDocID(i);
+      }
+
+      @Override
+      protected int comparePivot(int j) {
+        reader.getValue(j, scratch2);
+        int cmp = StringHelper.compare(numBytesToCompare, pivot.bytes, pivot.offset + offset, scratch2.bytes, scratch2.offset + offset);
+        if (cmp == 0) {
+          cmp = pivotDoc - reader.getDocID(j);
+        }
+        return cmp;
+      }
+    }.sort(from, to);
+  }
+
+  /** Partition points around {@code mid}. All values on the left must be less
+   *  than or equal to it and all values on the right must be greater than or
+   *  equal to it. */
+  static void partition(int maxDoc, int splitDim, int bytesPerDim, int commonPrefixLen,
+      MutablePointsReader reader, int from, int to, int mid,
+      BytesRef scratch1, BytesRef scratch2) {
+    final int offset = splitDim * bytesPerDim + commonPrefixLen;
+    final int cmpBytes = bytesPerDim - commonPrefixLen;
+    final int bitsPerDocId = PackedInts.bitsRequired(maxDoc - 1);
+    new RadixSelector(cmpBytes + (bitsPerDocId + 7) / 8) {
+
+      @Override
+      protected Selector getFallbackSelector(int k) {
+        return new IntroSelector() {
+
+          final BytesRef pivot = scratch1;
+          int pivotDoc;
+
+          @Override
+          protected void swap(int i, int j) {
+            reader.swap(i, j);
+          }
+
+          @Override
+          protected void setPivot(int i) {
+            reader.getValue(i, pivot);
+            pivotDoc = reader.getDocID(i);
+          }
+
+          @Override
+          protected int comparePivot(int j) {
+            if (k < cmpBytes) {
+              reader.getValue(j, scratch2);
+              int cmp = StringHelper.compare(cmpBytes - k, pivot.bytes, pivot.offset + offset + k, scratch2.bytes, scratch2.offset + offset + k);
+              if (cmp != 0) {
+                return cmp;
+              }
+            }
+            return pivotDoc - reader.getDocID(j);
+          }
+        };
+      }
+
+      @Override
+      protected void swap(int i, int j) {
+        reader.swap(i, j);
+      }
+
+      @Override
+      protected int byteAt(int i, int k) {
+        if (k < cmpBytes) {
+          return Byte.toUnsignedInt(reader.getByteAt(i, offset + k));
+        } else {
+          final int shift = bitsPerDocId - ((k - cmpBytes + 1) << 3);
+          return (reader.getDocID(i) >>> Math.max(0, shift)) & 0xff;
+        }
+      }
+    }.select(from, to, mid);
+  }
+}

lucene/core/src/test/org/apache/lucene/codecs/lucene60/TestLucene60PointsFormat.java

@@ -41,8 +41,9 @@ public class TestLucene60PointsFormat extends BasePointsFormatTestCase {
     if (random().nextBoolean()) {
       // randomize parameters
       int maxPointsInLeafNode = TestUtil.nextInt(random(), 50, 500);
+      double maxMBSortInHeap = 3.0 + (3*random().nextDouble());
       if (VERBOSE) {
-        System.out.println("TEST: using Lucene60PointsFormat with maxPointsInLeafNode=" + maxPointsInLeafNode);
+        System.out.println("TEST: using Lucene60PointsFormat with maxPointsInLeafNode=" + maxPointsInLeafNode + " and maxMBSortInHeap=" + maxMBSortInHeap);
       }
 
       // sneaky impersonation!
@@ -52,7 +53,7 @@ public class TestLucene60PointsFormat extends BasePointsFormatTestCase {
           return new PointsFormat() {
             @Override
             public PointsWriter fieldsWriter(SegmentWriteState writeState) throws IOException {
-              return new Lucene60PointsWriter(writeState, maxPointsInLeafNode);
+              return new Lucene60PointsWriter(writeState, maxPointsInLeafNode, maxMBSortInHeap);
             }
 
             @Override

lucene/core/src/test/org/apache/lucene/search/TestPointQueries.java

@@ -1156,8 +1156,9 @@ public class TestPointQueries extends LuceneTestCase {
   private static Codec getCodec() {
     if (Codec.getDefault().getName().equals("Lucene62")) {
       int maxPointsInLeafNode = TestUtil.nextInt(random(), 16, 2048);
+      double maxMBSortInHeap = 5.0 + (3*random().nextDouble());
       if (VERBOSE) {
-        System.out.println("TEST: using Lucene60PointsFormat with maxPointsInLeafNode=" + maxPointsInLeafNode);
+        System.out.println("TEST: using Lucene60PointsFormat with maxPointsInLeafNode=" + maxPointsInLeafNode + " and maxMBSortInHeap=" + maxMBSortInHeap);
       }
 
       return new FilterCodec("Lucene62", Codec.getDefault()) {
@@ -1166,7 +1167,7 @@ public class TestPointQueries extends LuceneTestCase {
           return new PointsFormat() {
             @Override
             public PointsWriter fieldsWriter(SegmentWriteState writeState) throws IOException {
-              return new Lucene60PointsWriter(writeState, maxPointsInLeafNode);
+              return new Lucene60PointsWriter(writeState, maxPointsInLeafNode, maxMBSortInHeap);
             }
 
             @Override

lucene/core/src/test/org/apache/lucene/util/TestByteBlockPool.java

@@ -45,7 +45,26 @@ public class TestByteBlockPool extends LuceneTestCase {
       for (BytesRef expected : list) {
         ref.grow(expected.length);
         ref.setLength(expected.length);
+        switch (random().nextInt(3)) {
+          case 0:
+            // copy bytes
             pool.readBytes(position, ref.bytes(), 0, ref.length());
+            break;
+          case 1:
+            // copy bytes one by one
+            for (int i = 0; i < ref.length(); ++i) {
+              ref.setByteAt(i, pool.readByte(position + i));
+            }
+            break;
+          case 2:
+            BytesRef scratch = new BytesRef();
+            scratch.length = ref.length();
+            pool.setRawBytesRef(scratch, position);
+            System.arraycopy(scratch.bytes, scratch.offset, ref.bytes(), 0, ref.length());
+            break;
+          default:
+            fail();
+        }
         assertEquals(expected, ref.get());
         position += ref.length();
       }

lucene/core/src/test/org/apache/lucene/util/TestIntroSelector.java

@@ -0,0 +1,86 @@
+/*
+ * 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.util;
+
+import java.util.Arrays;
+
+public class TestIntroSelector extends LuceneTestCase {
+
+  public void testSelect() {
+    for (int iter = 0; iter < 100; ++iter) {
+      doTestSelect(false);
+    }
+  }
+
+  public void testSlowSelect() {
+    for (int iter = 0; iter < 100; ++iter) {
+      doTestSelect(true);
+    }
+  }
+
+  private void doTestSelect(boolean slow) {
+    final int from = random().nextInt(5);
+    final int to = from + TestUtil.nextInt(random(), 1, 10000);
+    final int max = random().nextBoolean() ? random().nextInt(100) : random().nextInt(100000);
+    Integer[] arr = new Integer[from + to + random().nextInt(5)];
+    for (int i = 0; i < arr.length; ++i) {
+      arr[i] = TestUtil.nextInt(random(), 0, max);
+    }
+    final int k = TestUtil.nextInt(random(), from, to - 1);
+
+    Integer[] expected = arr.clone();
+    Arrays.sort(expected, from, to);
+
+    Integer[] actual = arr.clone();
+    IntroSelector selector = new IntroSelector() {
+
+      Integer pivot;
+
+      @Override
+      protected void swap(int i, int j) {
+        ArrayUtil.swap(actual, i, j);
+      }
+
+      @Override
+      protected void setPivot(int i) {
+        pivot = actual[i];
+      }
+
+      @Override
+      protected int comparePivot(int j) {
+        return pivot.compareTo(actual[j]);
+      }
+    };
+    if (slow) {
+      selector.slowSelect(from, to, k);
+    } else {
+      selector.select(from, to, k);
+    }
+
+    assertEquals(expected[k], actual[k]);
+    for (int i = 0; i < actual.length; ++i) {
+      if (i < from || i >= to) {
+        assertSame(arr[i], actual[i]);
+      } else if (i <= k) {
+        assertTrue(actual[i].intValue() <= actual[k].intValue());
+      } else {
+        assertTrue(actual[i].intValue() >= actual[k].intValue());
+      }
+    }
+  }
+
+}

lucene/core/src/test/org/apache/lucene/util/TestMSBRadixSorter.java

@@ -17,6 +17,8 @@
 package org.apache.lucene.util;
 
 import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
 
 public class TestMSBRadixSorter extends LuceneTestCase {
 
@@ -41,9 +43,12 @@ public class TestMSBRadixSorter extends LuceneTestCase {
         break;
     }
 
+    final int finalMaxLength = maxLength;
     new MSBRadixSorter(maxLength) {
 
+      @Override
       protected int byteAt(int i, int k) {
+        assertTrue(k < finalMaxLength);
         BytesRef ref = refs[i];
         if (ref.length <= k) {
           return -1;
@@ -114,4 +119,67 @@ public class TestMSBRadixSorter extends LuceneTestCase {
       testRandom(TestUtil.nextInt(random(), 1, 30), 2);
     }
   }
+
+  public void testRandom2() {
+    // how large our alphabet is
+    int letterCount = TestUtil.nextInt(random(), 2, 10);
+
+    // how many substring fragments to use
+    int substringCount = TestUtil.nextInt(random(), 2, 10);
+    Set<BytesRef> substringsSet = new HashSet<>();
+
+    // how many strings to make
+    int stringCount = atLeast(10000);
+
+    //System.out.println("letterCount=" + letterCount + " substringCount=" + substringCount + " stringCount=" + stringCount);
+    while(substringsSet.size() < substringCount) {
+      int length = TestUtil.nextInt(random(), 2, 10);
+      byte[] bytes = new byte[length];
+      for(int i=0;i<length;i++) {
+        bytes[i] = (byte) random().nextInt(letterCount);
+      }
+      BytesRef br = new BytesRef(bytes);
+      substringsSet.add(br);
+      //System.out.println("add substring count=" + substringsSet.size() + ": " + br);
+    }
+
+    BytesRef[] substrings = substringsSet.toArray(new BytesRef[substringsSet.size()]);
+    double[] chance = new double[substrings.length];
+    double sum = 0.0;
+    for(int i=0;i<substrings.length;i++) {
+      chance[i] = random().nextDouble();
+      sum += chance[i];
+    }
+
+    // give each substring a random chance of occurring:
+    double accum = 0.0;
+    for(int i=0;i<substrings.length;i++) {
+      accum += chance[i]/sum;
+      chance[i] = accum;
+    }
+
+    Set<BytesRef> stringsSet = new HashSet<>();
+    int iters = 0;
+    while (stringsSet.size() < stringCount && iters < stringCount*5) {
+      int count = TestUtil.nextInt(random(), 1, 5);
+      BytesRefBuilder b = new BytesRefBuilder();
+      for(int i=0;i<count;i++) {
+        double v = random().nextDouble();
+        accum = 0.0;
+        for(int j=0;j<substrings.length;j++) {
+          accum += chance[j];
+          if (accum >= v) {
+            b.append(substrings[j]);
+            break;
+          }
+        }
+      }
+      BytesRef br = b.toBytesRef();
+      stringsSet.add(br);
+      //System.out.println("add string count=" + stringsSet.size() + ": " + br);
+      iters++;
+    }
+
+    test(stringsSet.toArray(new BytesRef[stringsSet.size()]), stringsSet.size());
+  }
 }

lucene/core/src/test/org/apache/lucene/util/TestRadixSelector.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.util;
+
+import java.util.Arrays;
+
+public class TestRadixSelector extends LuceneTestCase {
+
+  public void testSelect() {
+    for (int iter = 0; iter < 100; ++iter) {
+      doTestSelect();
+    }
+  }
+
+  private void doTestSelect() {
+    final int from = random().nextInt(5);
+    final int to = from + TestUtil.nextInt(random(), 1, 10000);
+    final int maxLen = TestUtil.nextInt(random(), 1, 12);
+    BytesRef[] arr = new BytesRef[from + to + random().nextInt(5)];
+    for (int i = 0; i < arr.length; ++i) {
+      byte[] bytes = new byte[TestUtil.nextInt(random(), 0, maxLen)];
+      random().nextBytes(bytes);
+      arr[i] = new BytesRef(bytes);
+    }
+    doTest(arr, from, to, maxLen);
+  }
+
+  public void testSharedPrefixes() {
+    for (int iter = 0; iter < 100; ++iter) {
+      doTestSharedPrefixes();
+    }
+  }
+
+  private void doTestSharedPrefixes() {
+    final int from = random().nextInt(5);
+    final int to = from + TestUtil.nextInt(random(), 1, 10000);
+    final int maxLen = TestUtil.nextInt(random(), 1, 12);
+    BytesRef[] arr = new BytesRef[from + to + random().nextInt(5)];
+    for (int i = 0; i < arr.length; ++i) {
+      byte[] bytes = new byte[TestUtil.nextInt(random(), 0, maxLen)];
+      random().nextBytes(bytes);
+      arr[i] = new BytesRef(bytes);
+    }
+    final int sharedPrefixLength = Math.min(arr[0].length, TestUtil.nextInt(random(), 1, maxLen));
+    for (int i = 1; i < arr.length; ++i) {
+      System.arraycopy(arr[0].bytes, arr[0].offset, arr[i].bytes, arr[i].offset, Math.min(sharedPrefixLength, arr[i].length));
+    }
+    doTest(arr, from, to, maxLen);
+  }
+
+  private void doTest(BytesRef[] arr, int from, int to, int maxLen) {
+    final int k = TestUtil.nextInt(random(), from, to - 1);
+
+    BytesRef[] expected = arr.clone();
+    Arrays.sort(expected, from, to);
+
+    BytesRef[] actual = arr.clone();
+    final int enforcedMaxLen = random().nextBoolean() ? maxLen : Integer.MAX_VALUE;
+    RadixSelector selector = new RadixSelector(enforcedMaxLen) {
+
+      @Override
+      protected void swap(int i, int j) {
+        ArrayUtil.swap(actual, i, j);
+      }
+
+      @Override
+      protected int byteAt(int i, int k) {
+        assertTrue(k < enforcedMaxLen);
+        BytesRef b = actual[i];
+        if (k >= b.length) {
+          return -1;
+        } else {
+          return Byte.toUnsignedInt(b.bytes[b.offset + k]);
+        }
+      }
+
+    };
+    selector.select(from, to, k);
+
+    assertEquals(expected[k], actual[k]);
+    for (int i = 0; i < actual.length; ++i) {
+      if (i < from || i >= to) {
+        assertSame(arr[i], actual[i]);
+      } else if (i <= k) {
+        assertTrue(actual[i].compareTo(actual[k]) <= 0);
+      } else {
+        assertTrue(actual[i].compareTo(actual[k]) >= 0);
+      }
+    }
+  }
+
+}

lucene/core/src/test/org/apache/lucene/util/bkd/TestMutablePointsReaderUtils.java

@@ -0,0 +1,270 @@
+/*
+ * 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.util.bkd;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Comparator;
+
+import org.apache.lucene.codecs.MutablePointsReader;
+import org.apache.lucene.util.ArrayUtil;
+import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.LuceneTestCase;
+import org.apache.lucene.util.StringHelper;
+import org.apache.lucene.util.TestUtil;
+
+public class TestMutablePointsReaderUtils extends LuceneTestCase {
+
+  public void testSort() {
+    for (int iter = 0; iter < 5; ++iter) {
+      doTestSort();
+    }
+  }
+
+  private void doTestSort() {
+    final int bytesPerDim = TestUtil.nextInt(random(), 1, 16);
+    final int maxDoc = TestUtil.nextInt(random(), 1, 1 << random().nextInt(30));
+    Point[] points = createRandomPoints(1, bytesPerDim, maxDoc);
+    DummyPointsReader reader = new DummyPointsReader(points);
+    MutablePointsReaderUtils.sort(maxDoc, bytesPerDim, reader, 0, points.length);
+    Arrays.sort(points, new Comparator<Point>() {
+      @Override
+      public int compare(Point o1, Point o2) {
+        int cmp = o1.packedValue.compareTo(o2.packedValue);
+        if (cmp == 0) {
+          cmp = Integer.compare(o1.doc, o2.doc);
+        }
+        return cmp;
+      }
+    });
+    assertNotSame(points, reader.points);
+    assertArrayEquals(points, reader.points);
+  }
+
+  public void testSortByDim() {
+    for (int iter = 0; iter < 5; ++iter) {
+      doTestSortByDim();
+    }
+  }
+
+  private void doTestSortByDim() {
+    final int numDims = TestUtil.nextInt(random(), 1, 8);
+    final int bytesPerDim = TestUtil.nextInt(random(), 1, 16);
+    final int maxDoc = TestUtil.nextInt(random(), 1, 1 << random().nextInt(30));
+    Point[] points = createRandomPoints(numDims, bytesPerDim, maxDoc);
+    int[] commonPrefixLengths = new int[numDims];
+    for (int i = 0; i < commonPrefixLengths.length; ++i) {
+      commonPrefixLengths[i] = TestUtil.nextInt(random(), 0, bytesPerDim);
+    }
+    BytesRef firstValue = points[0].packedValue;
+    for (int i = 1; i < points.length; ++i) {
+      for (int dim = 0; dim < numDims; ++dim) {
+        int offset = dim * bytesPerDim;
+        BytesRef packedValue = points[i].packedValue;
+        System.arraycopy(firstValue.bytes, firstValue.offset + offset, packedValue.bytes, packedValue.offset + offset, commonPrefixLengths[dim]);
+      }
+    }
+    DummyPointsReader reader = new DummyPointsReader(points);
+    final int sortedDim = random().nextInt(numDims);
+    MutablePointsReaderUtils.sortByDim(sortedDim, bytesPerDim, commonPrefixLengths, reader, 0, points.length,
+        new BytesRef(), new BytesRef());
+    for (int i = 1; i < points.length; ++i) {
+      final int offset = sortedDim * bytesPerDim;
+      BytesRef previousValue = reader.points[i-1].packedValue;
+      BytesRef currentValue = reader.points[i].packedValue;
+      int cmp = StringHelper.compare(bytesPerDim,
+          previousValue.bytes, previousValue.offset + offset,
+          currentValue.bytes, currentValue.offset + offset);
+      if (cmp == 0) {
+        cmp = reader.points[i - 1].doc - reader.points[i].doc;
+      }
+      assertTrue(cmp <= 0);
+    }
+  }
+
+  public void testPartition() {
+    for (int iter = 0; iter < 5; ++iter) {
+      doTestPartition();
+    }
+  }
+
+  private void doTestPartition() {
+    final int numDims = TestUtil.nextInt(random(), 1, 8);
+    final int bytesPerDim = TestUtil.nextInt(random(), 1, 16);
+    final int maxDoc = TestUtil.nextInt(random(), 1, 1 << random().nextInt(30));
+    Point[] points = createRandomPoints(numDims, bytesPerDim, maxDoc);
+    int commonPrefixLength = TestUtil.nextInt(random(), 0, bytesPerDim);
+    final int splitDim =  random().nextInt(numDims);
+    BytesRef firstValue = points[0].packedValue;
+    for (int i = 1; i < points.length; ++i) {
+      BytesRef packedValue = points[i].packedValue;
+      int offset = splitDim * bytesPerDim;
+      System.arraycopy(firstValue.bytes, firstValue.offset + offset, packedValue.bytes, packedValue.offset + offset, commonPrefixLength);
+    }
+    DummyPointsReader reader = new DummyPointsReader(points);
+    final int pivot = TestUtil.nextInt(random(), 0, points.length - 1);
+    MutablePointsReaderUtils.partition(maxDoc, splitDim, bytesPerDim, commonPrefixLength, reader, 0, points.length, pivot,
+        new BytesRef(), new BytesRef());
+    BytesRef pivotValue = reader.points[pivot].packedValue;
+    int offset = splitDim * bytesPerDim;
+    for (int i = 0; i < points.length; ++i) {
+      BytesRef value = reader.points[i].packedValue;
+      int cmp = StringHelper.compare(bytesPerDim,
+          value.bytes, value.offset + offset,
+          pivotValue.bytes, pivotValue.offset + offset);
+      if (cmp == 0) {
+        cmp = reader.points[i].doc - reader.points[pivot].doc;
+      }
+      if (i < pivot) {
+        assertTrue(cmp <= 0);
+      } else if (i > pivot) {
+        assertTrue(cmp >= 0);
+      } else {
+        assertEquals(0, cmp);
+      }
+    }
+  }
+
+  private static Point[] createRandomPoints(int numDims, int bytesPerDim, int maxDoc) {
+    final int packedBytesLength = numDims * bytesPerDim;
+    final int numPoints = TestUtil.nextInt(random(), 1, 100000);
+    Point[] points = new Point[numPoints];
+    for (int i = 0; i < numPoints; ++i) {
+       byte[] value = new byte[packedBytesLength];
+       random().nextBytes(value);
+       points[i] = new Point(value, random().nextInt(maxDoc));
+    }
+    return points;
+  }
+
+  private static class Point {
+    final BytesRef packedValue;
+    final int doc;
+
+    Point(byte[] packedValue, int doc) {
+      // use a non-null offset to make sure MutablePointsReaderUtils does not ignore it
+      this.packedValue = new BytesRef(packedValue.length + 1);
+      this.packedValue.bytes[0] = (byte) random().nextInt(256);
+      this.packedValue.offset = 1;
+      this.packedValue.length = packedValue.length;
+      this.doc = doc;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (obj == null || obj instanceof Point == false) {
+        return false;
+      }
+      Point that = (Point) obj;
+      return packedValue.equals(that.packedValue) && doc == that.doc;
+    }
+
+    @Override
+    public int hashCode() {
+      return 31 * packedValue.hashCode() + doc;
+    }
+
+    @Override
+    public String toString() {
+      return "value=" + packedValue + " doc=" + doc;
+    }
+  }
+
+  private static class DummyPointsReader extends MutablePointsReader {
+
+    private final Point[] points;
+
+    DummyPointsReader(Point[] points) {
+      this.points = points.clone();
+    }
+
+    @Override
+    public void close() throws IOException {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public long ramBytesUsed() {
+      return 0;
+    }
+
+    @Override
+    public void getValue(int i, BytesRef packedValue) {
+      packedValue.bytes = points[i].packedValue.bytes;
+      packedValue.offset = points[i].packedValue.offset;
+      packedValue.length = points[i].packedValue.length;
+    }
+
+    @Override
+    public byte getByteAt(int i, int k) {
+      BytesRef packedValue = points[i].packedValue;
+      return packedValue.bytes[packedValue.offset + k];
+    }
+
+    @Override
+    public int getDocID(int i) {
+      return points[i].doc;
+    }
+
+    @Override
+    public void swap(int i, int j) {
+      ArrayUtil.swap(points, i, j);
+    }
+
+    @Override
+    public void checkIntegrity() throws IOException {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void intersect(String fieldName, IntersectVisitor visitor) throws IOException {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public byte[] getMinPackedValue(String fieldName) throws IOException {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public byte[] getMaxPackedValue(String fieldName) throws IOException {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public int getNumDimensions(String fieldName) throws IOException {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public int getBytesPerDimension(String fieldName) throws IOException {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public long size(String fieldName) {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public int getDocCount(String fieldName) {
+      throw new UnsupportedOperationException();
+    }
+
+  }
+
+}

lucene/ivy-versions.properties

@@ -106,6 +106,7 @@ io.netty.netty-all.version = 4.0.36.Final
 org.apache.curator.version = 2.8.0
 /org.apache.curator/curator-client = ${org.apache.curator.version}
 /org.apache.curator/curator-framework = ${org.apache.curator.version}
+/org.apache.curator/curator-recipes = ${org.apache.curator.version}
 
 /org.apache.derby/derby = 10.9.1.0
 

lucene/queries/src/java/org/apache/lucene/queries/function/valuesource/ComparisonBoolFunction.java

@@ -0,0 +1,105 @@
+/*
+ * 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.queries.function.valuesource;
+
+import java.io.IOException;
+import java.util.Map;
+
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.queries.function.FunctionValues;
+import org.apache.lucene.queries.function.ValueSource;
+import org.apache.lucene.queries.function.docvalues.BoolDocValues;
+import org.apache.lucene.search.IndexSearcher;
+
+/**
+ * Base class for comparison operators useful within an "if"/conditional.
+ */
+public abstract class ComparisonBoolFunction extends BoolFunction {
+
+  private final ValueSource lhs;
+  private final ValueSource rhs;
+  private final String name;
+
+  public ComparisonBoolFunction(ValueSource lhs, ValueSource rhs, String name) {
+    this.lhs = lhs;
+    this.rhs = rhs;
+    this.name = name;
+  }
+
+  /** Perform the comparison, returning true or false */
+  public abstract boolean compare(int doc, FunctionValues lhs, FunctionValues rhs);
+
+  /** Uniquely identify the operation (ie "gt", "lt" "gte", etc) */
+  public String name() {
+    return this.name;
+  }
+
+  @Override
+  public FunctionValues getValues(Map context, LeafReaderContext readerContext) throws IOException {
+    final FunctionValues lhsVal = this.lhs.getValues(context, readerContext);
+    final FunctionValues rhsVal = this.rhs.getValues(context, readerContext);
+    final String compLabel = this.name();
+
+    return new BoolDocValues(this) {
+      @Override
+      public boolean boolVal(int doc) {
+        return compare(doc, lhsVal, rhsVal);
+      }
+
+      @Override
+      public String toString(int doc) {
+        return compLabel + "(" + lhsVal.toString(doc) + "," + rhsVal.toString(doc) + ")";
+      }
+
+      @Override
+      public boolean exists(int doc) {
+        return lhsVal.exists(doc) && rhsVal.exists(doc);
+      }
+
+    };
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this.getClass() != o.getClass()) return false;
+    ComparisonBoolFunction other = (ComparisonBoolFunction)o;
+    return name().equals(other.name())
+        && lhs.equals(other.lhs)
+        && rhs.equals(other.rhs);  }
+
+  @Override
+  public int hashCode() {
+    int h = this.getClass().hashCode();
+    h = h * 31 + this.name().hashCode();
+    h = h * 31 + lhs.hashCode();
+    h = h * 31 + rhs.hashCode();
+    return h;
+  }
+
+  @Override
+  public String description() {
+      return name() + "(" + lhs.description() + "," + rhs.description() + ")";
+  }
+
+  @Override
+  public void createWeight(Map context, IndexSearcher searcher) throws IOException {
+    lhs.createWeight(context, searcher);
+    rhs.createWeight(context, searcher);
+  }
+
+}

lucene/replicator/src/java/org/apache/lucene/replicator/nrt/FileMetaData.java

@@ -38,5 +38,10 @@ public class FileMetaData {
     this.length = length;
     this.checksum = checksum;
   }
+
+  @Override
+  public String toString() {
+    return "FileMetaData(length=" + length + ")";
+  }
 }
 

lucene/replicator/src/test/org/apache/lucene/replicator/nrt/SimpleCopyJob.java

@@ -118,6 +118,8 @@ class SimpleCopyJob extends CopyJob {
       return highPriority ? -1 : 1;
     } else if (ord < other.ord) {
       return -1;
+    } else if (ord > other.ord) {
+      return 1;
     } else {
       return 0;
     }

lucene/spatial3d/src/java/org/apache/lucene/spatial3d/geom/Bounds.java

@@ -121,4 +121,11 @@ public interface Bounds {
    */
   public Bounds noBottomLatitudeBound();
   
+  /** Signal that there is no bound whatsoever.
+   * The bound is limited only by the constraints of the
+   * planet.
+   *@return the updated Bounds object.,
+   */
+  public Bounds noBound(final PlanetModel planetModel);
+  
 }

lucene/spatial3d/src/java/org/apache/lucene/spatial3d/geom/LatLonBounds.java

@@ -253,6 +253,11 @@ public class LatLonBounds implements Bounds {
     return this;
   }
 
+  @Override
+  public Bounds noBound(final PlanetModel planetModel) {
+    return noLongitudeBound().noTopLatitudeBound().noBottomLatitudeBound();
+  }
+  
   // Protected methods
   
   /** Update latitude bound.

lucene/spatial3d/src/java/org/apache/lucene/spatial3d/geom/Plane.java

@@ -1003,13 +1003,14 @@ public class Plane extends Vector {
    * D - MINIMUM_RESOLUTION.  Both are examined and intersection points determined.
    */
   protected void findIntersectionBounds(final PlanetModel planetModel, final Bounds boundsInfo, final Plane q, final Membership... bounds) {
+    //System.out.println("Finding intersection bounds");
     // Unnormalized, unchecked...
     final double lineVectorX = y * q.z - z * q.y;
     final double lineVectorY = z * q.x - x * q.z;
     final double lineVectorZ = x * q.y - y * q.x;
     if (Math.abs(lineVectorX) < MINIMUM_RESOLUTION && Math.abs(lineVectorY) < MINIMUM_RESOLUTION && Math.abs(lineVectorZ) < MINIMUM_RESOLUTION) {
       // Degenerate case: parallel planes
-      //System.err.println(" planes are parallel - no intersection");
+      //System.out.println(" planes are parallel - no intersection");
       return;
     }
 
@@ -1037,9 +1038,10 @@ public class Plane extends Vector {
     final double denomXZ = this.x * q.z - this.z * q.x;
     final double denomXY = this.x * q.y - this.y * q.x;
     if (Math.abs(denomYZ) >= Math.abs(denomXZ) && Math.abs(denomYZ) >= Math.abs(denomXY)) {
+      //System.out.println("X biggest");
       // X is the biggest, so our point will have x0 = 0.0
       if (Math.abs(denomYZ) < MINIMUM_RESOLUTION_SQUARED) {
-        //System.err.println(" Denominator is zero: no intersection");
+        //System.out.println(" Denominator is zero: no intersection");
         return;
       }
       final double denom = 1.0 / denomYZ;
@@ -1061,9 +1063,10 @@ public class Plane extends Vector {
         0.0, (-(this.D-MINIMUM_RESOLUTION) * q.z - this.z * -(q.D-MINIMUM_RESOLUTION)) * denom, (this.y * -(q.D-MINIMUM_RESOLUTION) + (this.D-MINIMUM_RESOLUTION) * q.y) * denom,
         bounds);
     } else if (Math.abs(denomXZ) >= Math.abs(denomXY) && Math.abs(denomXZ) >= Math.abs(denomYZ)) {
+      //System.out.println("Y biggest");
       // Y is the biggest, so y0 = 0.0
       if (Math.abs(denomXZ) < MINIMUM_RESOLUTION_SQUARED) {
-        //System.err.println(" Denominator is zero: no intersection");
+        //System.out.println(" Denominator is zero: no intersection");
         return;
       }
       final double denom = 1.0 / denomXZ;
@@ -1084,9 +1087,10 @@ public class Plane extends Vector {
         (-(this.D-MINIMUM_RESOLUTION) * q.z - this.z * -(q.D-MINIMUM_RESOLUTION)) * denom, 0.0, (this.x * -(q.D-MINIMUM_RESOLUTION) + (this.D-MINIMUM_RESOLUTION) * q.x) * denom,
         bounds);
     } else {
+      //System.out.println("Z biggest");
       // Z is the biggest, so Z0 = 0.0
       if (Math.abs(denomXY) < MINIMUM_RESOLUTION_SQUARED) {
-        //System.err.println(" Denominator is zero: no intersection");
+        //System.out.println(" Denominator is zero: no intersection");
         return;
       }
       final double denom = 1.0 / denomXY;
@@ -1178,6 +1182,10 @@ public class Plane extends Vector {
       if (point2Valid) {
         boundsInfo.addPoint(new GeoPoint(point2X, point2Y, point2Z));
       }
+    } else {
+      // If we can't intersect line with world, then it's outside the world, so
+      // we have to assume everything is included.
+      boundsInfo.noBound(planetModel);
     }
   }
 
@@ -1351,8 +1359,6 @@ public class Plane extends Vector {
       // m * [- 2*A*ab^2*r + 2*A^2*ab^2*r*q + 2*B^2*ab^2*r*q + 2*C^2*c^2*r*q] +
       // [ab^2 - 2*A*ab^2*q + A^2*ab^2*q^2 + B^2*ab^2*q^2 + C^2*c^2*q^2]  =  0
       
-      //System.err.println("    computing X bound");
-      
       // Useful subexpressions for this bound
       final double q = A*abSquared*k;
       final double qSquared = q * q;
@@ -1392,6 +1398,7 @@ public class Plane extends Vector {
           assert Math.abs(a * m1 * m1 + b * m1 + c) < MINIMUM_RESOLUTION;
           final double m2 = (-b - sqrtResult) * commonDenom;
           assert Math.abs(a * m2 * m2 + b * m2 + c) < MINIMUM_RESOLUTION;
+          if (Math.abs(m1) >= MINIMUM_RESOLUTION || Math.abs(m2) >= MINIMUM_RESOLUTION) {
             final double l1 = r * m1 + q;
             final double l2 = r * m2 + q;
             // x = ((1 - l*A) * ab^2 ) / (2 * m)
@@ -1410,11 +1417,14 @@ public class Plane extends Vector {
             //assert evaluateIsZero(thePoint2): "Evaluation of point2: "+evaluate(thePoint2);
             addPoint(boundsInfo, bounds, thePoint1);
             addPoint(boundsInfo, bounds, thePoint2);
+          } else {
+            // This is a plane of the form A=n B=0 C=0.  We can set a bound only by noting the D value.
+            boundsInfo.addXValue(-D/A);
+          }
         } else {
           // No solutions
         }
       } else if (Math.abs(b) > MINIMUM_RESOLUTION_SQUARED) {
-        //System.err.println("Not x quadratic");
         // a = 0, so m = - c / b
         final double m = -c / b;
         final double l = r * m + q;
@@ -1561,6 +1571,7 @@ public class Plane extends Vector {
           assert Math.abs(a * m1 * m1 + b * m1 + c) < MINIMUM_RESOLUTION;
           final double m2 = (-b - sqrtResult) * commonDenom;
           assert Math.abs(a * m2 * m2 + b * m2 + c) < MINIMUM_RESOLUTION;
+          if (Math.abs(m1) >= MINIMUM_RESOLUTION || Math.abs(m2) >= MINIMUM_RESOLUTION) {
             final double l1 = r * m1 + q;
             final double l2 = r * m2 + q;
             // x = (-l*A * ab^2 ) / (2 * m)
@@ -1579,6 +1590,10 @@ public class Plane extends Vector {
             //assert evaluateIsZero(thePoint2): "Evaluation of point2: "+evaluate(thePoint2);
             addPoint(boundsInfo, bounds, thePoint1);
             addPoint(boundsInfo, bounds, thePoint2);
+          } else {
+            // This is a plane of the form A=0 B=n C=0.  We can set a bound only by noting the D value.
+            boundsInfo.addYValue(-D/B);
+          }
         } else {
           // No solutions
         }

lucene/spatial3d/src/java/org/apache/lucene/spatial3d/geom/XYZBounds.java

@@ -292,6 +292,17 @@ public class XYZBounds implements Bounds {
     return this;
   }
 
+  @Override
+  public Bounds noBound(final PlanetModel planetModel) {
+    minX = planetModel.getMinimumXValue();
+    maxX = planetModel.getMaximumXValue();
+    minY = planetModel.getMinimumYValue();
+    maxY = planetModel.getMaximumYValue();
+    minZ = planetModel.getMinimumZValue();
+    maxZ = planetModel.getMaximumZValue();
+    return this;
+  }
+
   @Override
   public String toString() {
     return "XYZBounds: [xmin="+minX+" xmax="+maxX+" ymin="+minY+" ymax="+maxY+" zmin="+minZ+" zmax="+maxZ+"]";

lucene/spatial3d/src/test/org/apache/lucene/spatial3d/TestGeo3DPoint.java

@@ -87,8 +87,9 @@ public class TestGeo3DPoint extends LuceneTestCase {
   private static Codec getCodec() {
     if (Codec.getDefault().getName().equals("Lucene62")) {
       int maxPointsInLeafNode = TestUtil.nextInt(random(), 16, 2048);
+      double maxMBSortInHeap = 3.0 + (3*random().nextDouble());
       if (VERBOSE) {
-        System.out.println("TEST: using Lucene60PointsFormat with maxPointsInLeafNode=" + maxPointsInLeafNode);
+        System.out.println("TEST: using Lucene60PointsFormat with maxPointsInLeafNode=" + maxPointsInLeafNode + " and maxMBSortInHeap=" + maxMBSortInHeap);
       }
 
       return new FilterCodec("Lucene62", Codec.getDefault()) {
@@ -97,7 +98,7 @@ public class TestGeo3DPoint extends LuceneTestCase {
           return new PointsFormat() {
             @Override
             public PointsWriter fieldsWriter(SegmentWriteState writeState) throws IOException {
-              return new Lucene60PointsWriter(writeState, maxPointsInLeafNode);
+              return new Lucene60PointsWriter(writeState, maxPointsInLeafNode, maxMBSortInHeap);
             }
 
             @Override

lucene/spatial3d/src/test/org/apache/lucene/spatial3d/geom/GeoBBoxTest.java

@@ -372,4 +372,19 @@ public class GeoBBoxTest {
     assertTrue(box.isWithin(point)?solid.isWithin(point):true);
   }
   
+  @Test
+  public void testFailureCase2() {
+    //final GeoPoint point = new GeoPoint(-0.7375647084975573, -2.3309121299774915E-10, 0.6746626163258577);
+    final GeoPoint point = new GeoPoint(-0.737564708579924, -9.032562595264542E-17, 0.6746626165197899);
+    final GeoBBox box = new GeoRectangle(PlanetModel.WGS84, 0.7988584710911523, 0.25383311815493353, -1.2236144735575564E-12, 7.356011300929654E-49);
+    final XYZBounds bounds = new XYZBounds();
+    box.getBounds(bounds);
+    final XYZSolid solid = XYZSolidFactory.makeXYZSolid(PlanetModel.WGS84, bounds.getMinimumX(), bounds.getMaximumX(), bounds.getMinimumY(), bounds.getMaximumY(), bounds.getMinimumZ(), bounds.getMaximumZ());
+
+    //System.out.println("Is within Y value? "+(point.y >= bounds.getMinimumY() && point.y <= bounds.getMaximumY()));
+    //System.out.println("Shape = "+box+" is within? "+box.isWithin(point));
+    //System.out.println("XYZBounds = "+bounds+" is within? "+solid.isWithin(point)+" solid="+solid);
+    assertTrue(box.isWithin(point) == solid.isWithin(point));
+  }
+  
 }

lucene/spatial3d/src/test/org/apache/lucene/spatial3d/geom/GeoCircleTest.java

@@ -405,4 +405,18 @@ public class GeoCircleTest extends LuceneTestCase {
     assertTrue(solid.isWithin(gp));
   }
   
+  @Test
+  public void testBoundsFailureCase2() {
+    final GeoCircle gc = GeoCircleFactory.makeGeoCircle(PlanetModel.WGS84, -2.7574435614238194E-13, 0.0, 1.5887859182593391);
+    final GeoPoint gp = new GeoPoint(PlanetModel.WGS84, 0.7980359504429014, 1.5964981068121482);
+    final XYZBounds bounds = new XYZBounds();
+    gc.getBounds(bounds);
+    System.out.println("Bounds = "+bounds);
+    System.out.println("Point = "+gp);
+    final XYZSolid solid = XYZSolidFactory.makeXYZSolid(PlanetModel.WGS84, bounds.getMinimumX(), bounds.getMaximumX(), bounds.getMinimumY(), bounds.getMaximumY(), bounds.getMinimumZ(), bounds.getMaximumZ());
+    
+    assert gc.isWithin(gp)?solid.isWithin(gp):true;
+    
+  }
+  
 }

lucene/test-framework/src/java/org/apache/lucene/codecs/asserting/AssertingPointsFormat.java

@@ -126,6 +126,7 @@ public final class AssertingPointsFormat extends PointsFormat {
           assert false: "point values are out of order";
         }
         System.arraycopy(packedValue, 0, lastDocValue, 0, bytesPerDim);
+        lastDocID = docID;
       }
       in.visit(docID, packedValue);
     }
@@ -254,11 +255,11 @@ public final class AssertingPointsFormat extends PointsFormat {
     }
     
     @Override
-    public void writeField(FieldInfo fieldInfo, PointsReader values, double maxMBSortInHeap) throws IOException {
+    public void writeField(FieldInfo fieldInfo, PointsReader values) throws IOException {
       if (fieldInfo.getPointDimensionCount() == 0) {
         throw new IllegalArgumentException("writing field=\"" + fieldInfo.name + "\" but pointDimensionalCount is 0");
       }
-      in.writeField(fieldInfo, values, maxMBSortInHeap);
+      in.writeField(fieldInfo, values);
     }
 
     @Override

lucene/test-framework/src/java/org/apache/lucene/codecs/cranky/CrankyPointsFormat.java

@@ -56,11 +56,11 @@ class CrankyPointsFormat extends PointsFormat {
     }
 
     @Override
-    public void writeField(FieldInfo fieldInfo, PointsReader values, double maxMBSortInHeap) throws IOException {
+    public void writeField(FieldInfo fieldInfo, PointsReader values) throws IOException {
       if (random.nextInt(100) == 0) {
         throw new IOException("Fake IOException");
       }  
-      delegate.writeField(fieldInfo, values, maxMBSortInHeap);
+      delegate.writeField(fieldInfo, values);
     }
 
     @Override

lucene/test-framework/src/java/org/apache/lucene/geo/BaseGeoPointTestCase.java

@@ -67,6 +67,7 @@ import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.SloppyMath;
 import org.apache.lucene.util.TestUtil;
+import org.apache.lucene.util.bkd.BKDWriter;
 
 /**
  * Abstract class to do basic tests for a geospatial impl (high level
@@ -1247,7 +1248,7 @@ public abstract class BaseGeoPointTestCase extends LuceneTestCase {
         return new PointsFormat() {
           @Override
           public PointsWriter fieldsWriter(SegmentWriteState writeState) throws IOException {
-            return new Lucene60PointsWriter(writeState, pointsInLeaf);
+            return new Lucene60PointsWriter(writeState, pointsInLeaf, BKDWriter.DEFAULT_MAX_MB_SORT_IN_HEAP);
           }
   
           @Override

lucene/test-framework/src/java/org/apache/lucene/index/RandomCodec.java

@@ -92,6 +92,7 @@ public class RandomCodec extends AssertingCodec {
   // which is less effective for testing.
   // TODO: improve how we randomize this...
   private final int maxPointsInLeafNode;
+  private final double maxMBSortInHeap;
   private final int bkdSplitRandomSeed;
 
   @Override
@@ -102,9 +103,9 @@ public class RandomCodec extends AssertingCodec {
 
         // Randomize how BKDWriter chooses its splis:
 
-        return new Lucene60PointsWriter(writeState, maxPointsInLeafNode) {
+        return new Lucene60PointsWriter(writeState, maxPointsInLeafNode, maxMBSortInHeap) {
           @Override
-          public void writeField(FieldInfo fieldInfo, PointsReader values, double maxMBSortInHeap) throws IOException {
+          public void writeField(FieldInfo fieldInfo, PointsReader values) throws IOException {
 
             boolean singleValuePerDoc = values.size(fieldInfo.name) == values.getDocCount(fieldInfo.name);
 
@@ -184,6 +185,7 @@ public class RandomCodec extends AssertingCodec {
     int lowFreqCutoff = TestUtil.nextInt(random, 2, 100);
 
     maxPointsInLeafNode = TestUtil.nextInt(random, 16, 2048);
+    maxMBSortInHeap = 5.0 + (3*random.nextDouble());
     bkdSplitRandomSeed = random.nextInt();
 
     add(avoidCodecs,
@@ -251,7 +253,8 @@ public class RandomCodec extends AssertingCodec {
   public String toString() {
     return super.toString() + ": " + previousMappings.toString() +
            ", docValues:" + previousDVMappings.toString() +
-           ", maxPointsInLeafNode=" + maxPointsInLeafNode;
+           ", maxPointsInLeafNode=" + maxPointsInLeafNode +
+           ", maxMBSortInHeap=" + maxMBSortInHeap;
   }
 
   /** Just like {@link BKDWriter} except it evilly picks random ways to split cells on

lucene/test-framework/src/java/org/apache/lucene/store/MockDirectoryWrapper.java

@@ -771,7 +771,7 @@ public class MockDirectoryWrapper extends BaseDirectoryWrapper {
       }
       ii = new SlowOpeningMockIndexInputWrapper(this, name, delegateInput);
     } else {
-      ii = new MockIndexInputWrapper(this, name, delegateInput);
+      ii = new MockIndexInputWrapper(this, name, delegateInput, null);
     }
     addFileHandle(ii, name, Handle.Input);
     return ii;

lucene/test-framework/src/java/org/apache/lucene/store/MockIndexInputWrapper.java

@@ -30,12 +30,19 @@ public class MockIndexInputWrapper extends IndexInput {
   private MockDirectoryWrapper dir;
   final String name;
   private IndexInput delegate;
-  private boolean isClone;
-  private boolean closed;
+  private volatile boolean closed;
 
-  /** Construct an empty output buffer. */
-  public MockIndexInputWrapper(MockDirectoryWrapper dir, String name, IndexInput delegate) {
+  // Which MockIndexInputWrapper we were cloned from, or null if we are not a clone:
+  private final MockIndexInputWrapper parent;
+  
+  /** Sole constructor */
+  public MockIndexInputWrapper(MockDirectoryWrapper dir, String name, IndexInput delegate, MockIndexInputWrapper parent) {
     super("MockIndexInputWrapper(name=" + name + " delegate=" + delegate + ")");
+
+    // If we are a clone then our parent better not be a clone!
+    assert parent == null || parent.parent == null;
+    
+    this.parent = parent;
     this.name = name;
     this.dir = dir;
     this.delegate = delegate;
@@ -54,7 +61,7 @@ public class MockIndexInputWrapper extends IndexInput {
       // remove the conditional check so we also track that
       // all clones get closed:
       assert delegate != null;
-      if (!isClone) {
+      if (parent == null) {
         dir.removeIndexInput(this, name);
       }
       dir.maybeThrowDeterministicException();
@@ -62,9 +69,13 @@ public class MockIndexInputWrapper extends IndexInput {
   }
   
   private void ensureOpen() {
+    // TODO: not great this is a volatile read (closed) ... we should deploy heavy JVM voodoo like SwitchPoint to avoid this
     if (closed) {
       throw new RuntimeException("Abusing closed IndexInput!");
     }
+    if (parent != null && parent.closed) {
+      throw new RuntimeException("Abusing clone of a closed IndexInput!");
+    }
   }
 
   @Override
@@ -75,8 +86,7 @@ public class MockIndexInputWrapper extends IndexInput {
     }
     dir.inputCloneCount.incrementAndGet();
     IndexInput iiclone = delegate.clone();
-    MockIndexInputWrapper clone = new MockIndexInputWrapper(dir, name, iiclone);
-    clone.isClone = true;
+    MockIndexInputWrapper clone = new MockIndexInputWrapper(dir, name, iiclone, parent != null ? parent : this);
     // Pending resolution on LUCENE-686 we may want to
     // uncomment this code so that we also track that all
     // clones get closed:
@@ -102,8 +112,7 @@ public class MockIndexInputWrapper extends IndexInput {
     }
     dir.inputCloneCount.incrementAndGet();
     IndexInput slice = delegate.slice(sliceDescription, offset, length);
-    MockIndexInputWrapper clone = new MockIndexInputWrapper(dir, sliceDescription, slice);
-    clone.isClone = true;
+    MockIndexInputWrapper clone = new MockIndexInputWrapper(dir, sliceDescription, slice, parent != null ? parent : this);
     return clone;
   }
 

lucene/test-framework/src/java/org/apache/lucene/store/SlowClosingMockIndexInputWrapper.java

@@ -30,7 +30,7 @@ class SlowClosingMockIndexInputWrapper extends MockIndexInputWrapper {
 
   public SlowClosingMockIndexInputWrapper(MockDirectoryWrapper dir,
       String name, IndexInput delegate) {
-    super(dir, name, delegate);
+    super(dir, name, delegate, null);
   }
   
   @Override

lucene/test-framework/src/java/org/apache/lucene/store/SlowOpeningMockIndexInputWrapper.java

@@ -28,7 +28,7 @@ class SlowOpeningMockIndexInputWrapper extends MockIndexInputWrapper {
 
   public SlowOpeningMockIndexInputWrapper(MockDirectoryWrapper dir,
       String name, IndexInput delegate) throws IOException {
-    super(dir, name, delegate);
+    super(dir, name, delegate, null);
     try {
       Thread.sleep(50);
     } catch (InterruptedException ie) {

lucene/test-framework/src/test/org/apache/lucene/store/TestMockDirectoryWrapper.java

@@ -171,4 +171,40 @@ public class TestMockDirectoryWrapper extends BaseDirectoryTestCase {
 
     assertTrue("MockDirectoryWrapper on dir=" + dir + " failed to corrupt an unsync'd file", changed);
   }
+
+  public void testAbuseClosedIndexInput() throws Exception {
+    MockDirectoryWrapper dir = newMockDirectory();
+    IndexOutput out = dir.createOutput("foo", IOContext.DEFAULT);
+    out.writeByte((byte) 42);
+    out.close();
+    final IndexInput in = dir.openInput("foo", IOContext.DEFAULT);
+    in.close();
+    expectThrows(RuntimeException.class, in::readByte);
+    dir.close();
+  }
+
+  public void testAbuseCloneAfterParentClosed() throws Exception {
+    MockDirectoryWrapper dir = newMockDirectory();
+    IndexOutput out = dir.createOutput("foo", IOContext.DEFAULT);
+    out.writeByte((byte) 42);
+    out.close();
+    IndexInput in = dir.openInput("foo", IOContext.DEFAULT);
+    final IndexInput clone = in.clone();
+    in.close();
+    expectThrows(RuntimeException.class, clone::readByte);
+    dir.close();
+  }
+
+  public void testAbuseCloneOfCloneAfterParentClosed() throws Exception {
+    MockDirectoryWrapper dir = newMockDirectory();
+    IndexOutput out = dir.createOutput("foo", IOContext.DEFAULT);
+    out.writeByte((byte) 42);
+    out.close();
+    IndexInput in = dir.openInput("foo", IOContext.DEFAULT);
+    IndexInput clone1 = in.clone();
+    IndexInput clone2 = clone1.clone();
+    in.close();
+    expectThrows(RuntimeException.class, clone2::readByte);
+    dir.close();
+  }
 }

solr/CHANGES.txt

@@ -100,6 +100,25 @@ New Features
 * SOLR-9275: XML QueryParser support (defType=xmlparser) now extensible via configuration.
   (Christine Poerschke)
 
+* SOLR-9200: Add Delegation Token Support to Solr.
+  (Gregory Chanan)
+
+* SOLR-9038: Solr core snapshots: The current commit can be snapshotted which retains the commit and associates it with
+  a name.  The core admin API can create snapshots, list them, and delete them. Snapshot names can be referenced in
+  doing a core backup, and in replication.  Snapshot metadata is stored in a new snapshot_metadata/ dir.
+  (Hrishikesh Gadre via David Smiley)
+
+* SOLR-9279: New boolean comparison function queries comparing numeric arguments: gt, gte, lt, lte, eq
+  (Doug Turnbull, David Smiley)
+
+* SOLR-9324: Support Secure Impersonation / Proxy User for solr authentication
+  (Gregory Chanan)
+
+* SOLR-9252: Feature selection and logistic regression on text (Cao Manh Dat, Joel Bernstein)
+
+* SOLR-6465: CDCR: fall back to whole-index replication when tlogs are insufficient.
+  (Noble Paul, Renaud Delbru, shalin)
+
 * SOLR-9320: A REPLACENODE command to decommission an existing node with another new node
    (noble, Nitin Sharma, Varun Thacker)
 
@@ -170,6 +189,19 @@ Bug Fixes
 
 * SOLR-9339: NPE in CloudSolrClient when the response is null (noble)
 
+* SOLR-8596: Web UI doesn't correctly generate queries which include local parameters (Alexandre Rafalovitch, janhoy)
+
+* SOLR-8645: managed-schema is now syntax highlighted in cloud->Tree view (Alexandre Rafalovitch via janhoy)
+
+* SOLR-8379: UI Cloud->Tree view now shows .txt files correctly (Alexandre Rafalovitch via janhoy)
+
+* SOLR-9003: New Admin UI's Dataimport screen now correctly displays DIH Debug output (Alexandre Rafalovitch)
+
+* SOLR-9308: Fix distributed RTG to forward request params, fixes fq and non-default fl params (hossman)
+
+* SOLR-9179: NPE in IndexSchema using IBM JDK (noble, Colvin Cowie)
+
+* SOLR-9397: Config API does not support adding caches (noble)
 
 Optimizations
 ----------------------
@@ -179,6 +211,13 @@ Optimizations
 * SOLR-9264: Optimize ZkController.publishAndWaitForDownStates to not read all collection states and
   watch relevant collections instead. (Hrishikesh Gadre, shalin)
 
+* SOLR-9335: Solr cache/search/update stats counters now use LongAdder which are supposed to have higher throughput
+  under high contention. (Varun Thacker)
+
+* SOLR-9350: JSON Facets: method="stream" will no longer always uses & populates the filter cache, likely
+  flushing it.  'cacheDf' can be configured to set a doc frequency threshold, now defaulting to 1/16th doc count.
+  Using -1 Disables use of the cache. (David Smiley, yonik)
+
 Other Changes
 ----------------------
 
@@ -202,6 +241,25 @@ Other Changes
 * SOLR-9163: Sync up basic_configs and data_driven_schema_configs, removing almost all differences
   except what is required for schemaless. (yonik)
 
+* SOLR-9340: Change ZooKeeper disconnect and session expiry related logging from INFO to WARN to
+  make debugging easier (Varun Thacker)
+
+* SOLR-9358: [AngularUI] In Cloud->Tree file view area, collapse metadata by default (janhoy)
+
+* SOLR-9256: asserting hasNext() contract in JdbcDataSource in DataImportHandler (Kristine Jetzke via Mikhai Khludnev)
+
+* SOLR-9209: extracting JdbcDataSource.createResultSetIterator() for extension (Kristine Jetzke via Mikhai Khludnev)
+
+* SOLR-9353: Factor out ReRankQParserPlugin.ReRankQueryRescorer private class. (Christine Poerschke)
+
+* SOLR-9392: Fixed CDCR Test failures which were due to leaked resources. (shalin)
+
+* SOLR-9385: Add QParser.getParser(String,SolrQueryRequest) variant. (Christine Poerschke)
+
+* SOLR-9367: Improved TestInjection's randomization logic to use LuceneTestCase.random() (hossman)
+
+* SOLR-9331: Remove ReRankQuery's length constructor argument and member. (Christine Poerschke)
+
 ==================  6.1.0 ==================
 
 Consult the LUCENE_CHANGES.txt file for additional, low level, changes in this release.

solr/contrib/analytics/src/java/org/apache/solr/analytics/accumulator/FacetingAccumulator.java

@@ -604,7 +604,7 @@ public class FacetingAccumulator extends BasicAccumulator implements FacetValueA
         QueryFacetAccumulator qAcc = new QueryFacetAccumulator(this,qfr.getName(),query);
         final Query q;
         try {
-          q = QParser.getParser(query, null, queryRequest).getQuery();
+          q = QParser.getParser(query, queryRequest).getQuery();
         } catch( SyntaxError e ){
           throw new SolrException(ErrorCode.BAD_REQUEST,"Invalid query '"+query+"'",e);
         }

solr/contrib/dataimporthandler/src/java/org/apache/solr/handler/dataimport/JdbcDataSource.java

@@ -280,10 +280,14 @@ public class JdbcDataSource extends
       resultSetIterator.close();
       resultSetIterator = null;
     }
-    resultSetIterator = new ResultSetIterator(query);
+    resultSetIterator = createResultSetIterator(query);
     return resultSetIterator.getIterator();
   }
 
+  protected ResultSetIterator createResultSetIterator(String query) {
+    return new ResultSetIterator(query);
+  }
+
   private void logError(String msg, Exception e) {
     LOG.warn(msg, e);
   }

solr/contrib/dataimporthandler/src/test/org/apache/solr/handler/dataimport/TestJdbcDataSource.java

@@ -510,6 +510,45 @@ public class TestJdbcDataSource extends AbstractDataImportHandlerTestCase {
       DriverManager.deregisterDriver(driver);
     }
   }
+  
+  
+  @Test
+  public void testEmptyResultSet() throws Exception {
+      MockInitialContextFactory.bind("java:comp/env/jdbc/JndiDB", dataSource);
+
+      props.put(JdbcDataSource.JNDI_NAME, "java:comp/env/jdbc/JndiDB");
+      EasyMock.expect(dataSource.getConnection()).andReturn(connection);
+
+      jdbcDataSource.init(context, props);
+
+      connection.setAutoCommit(false);
+
+      Statement statement = mockControl.createMock(Statement.class);
+      EasyMock.expect(connection.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY))
+          .andReturn(statement);
+      statement.setFetchSize(500);
+      statement.setMaxRows(0);
+      EasyMock.expect(statement.execute("query")).andReturn(true);
+      ResultSet resultSet = mockControl.createMock(ResultSet.class);
+      EasyMock.expect(statement.getResultSet()).andReturn(resultSet);
+      ResultSetMetaData metaData = mockControl.createMock(ResultSetMetaData.class);
+      EasyMock.expect(resultSet.getMetaData()).andReturn(metaData);
+      EasyMock.expect(metaData.getColumnCount()).andReturn(0);
+      EasyMock.expect(resultSet.next()).andReturn(false);
+      resultSet.close();
+      EasyMock.expect(statement.getMoreResults()).andReturn(false);
+      EasyMock.expect(statement.getUpdateCount()).andReturn(-1);
+      statement.close();
+
+      mockControl.replay();
+
+      Iterator<Map<String,Object>> resultSetIterator = jdbcDataSource.getData("query");
+      resultSetIterator.hasNext();
+      resultSetIterator.hasNext();
+
+      mockControl.verify();
+  }
+  
   @Test
   @Ignore("Needs a Mock database server to work")
   public void testBasic() throws Exception {

solr/contrib/map-reduce/src/java/org/apache/solr/hadoop/ZooKeeperInspector.java

@@ -16,6 +16,15 @@
  */
 package org.apache.solr.hadoop;
 
+import java.io.File;
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
 import com.google.common.io.Files;
 import org.apache.commons.io.FileUtils;
 import org.apache.solr.cloud.ZkController;
@@ -35,15 +44,6 @@ import org.apache.zookeeper.KeeperException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.File;
-import java.io.IOException;
-import java.lang.invoke.MethodHandles;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.Comparator;
-import java.util.List;
-
 /**
  * Extracts SolrCloud information from ZooKeeper.
  */
@@ -78,8 +78,7 @@ final class ZooKeeperInspector {
     }
     SolrZkClient zkClient = getZkClient(zkHost);
     
-    try {
-      ZkStateReader zkStateReader = new ZkStateReader(zkClient);
+    try (ZkStateReader zkStateReader = new ZkStateReader(zkClient)) {
       try {
         // first check for alias
         collection = checkForAlias(zkClient, collection);

solr/core/ivy.xml

@@ -134,6 +134,10 @@
     <dependency org="antlr" name="antlr" rev="${/antlr/antlr}" conf="test.MiniKdc"/>
     <dependency org="net.sf.ehcache" name="ehcache-core" rev="${/net.sf.ehcache/ehcache-core}" conf="test.MiniKdc"/>
 
+    <dependency org="org.apache.curator" name="curator-framework" rev="${/org.apache.curator/curator-framework}" conf="compile"/>
+    <dependency org="org.apache.curator" name="curator-client" rev="${/org.apache.curator/curator-client}" conf="compile"/>
+    <dependency org="org.apache.curator" name="curator-recipes" rev="${/org.apache.curator/curator-recipes}" conf="compile"/>
+
     <!-- StatsComponents percentiles Dependencies-->
     <dependency org="com.tdunning" name="t-digest" rev="${/com.tdunning/t-digest}" conf="compile->*"/>
     <!-- SQL Parser -->

solr/core/src/java/org/apache/solr/core/IndexDeletionPolicyWrapper.java

@@ -15,21 +15,26 @@
  * limitations under the License.
  */
 package org.apache.solr.core;
+
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
 import org.apache.lucene.index.IndexCommit;
 import org.apache.lucene.index.IndexDeletionPolicy;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.store.Directory;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager;
 import org.apache.solr.update.SolrIndexWriter;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.IOException;
-import java.lang.invoke.MethodHandles;
-import java.util.*;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
-
 /**
  * A wrapper for an IndexDeletionPolicy instance.
  * <p>
@@ -52,9 +57,11 @@ public final class IndexDeletionPolicyWrapper extends IndexDeletionPolicy {
   private final Map<Long, Long> reserves = new ConcurrentHashMap<>();
   private volatile IndexCommit latestCommit;
   private final ConcurrentHashMap<Long, AtomicInteger> savedCommits = new ConcurrentHashMap<>();
+  private final SolrSnapshotMetaDataManager snapshotMgr;
 
-  public IndexDeletionPolicyWrapper(IndexDeletionPolicy deletionPolicy) {
+  public IndexDeletionPolicyWrapper(IndexDeletionPolicy deletionPolicy, SolrSnapshotMetaDataManager snapshotMgr) {
     this.deletionPolicy = deletionPolicy;
+    this.snapshotMgr = snapshotMgr;
   }
 
   /**
@@ -134,7 +141,6 @@ public final class IndexDeletionPolicyWrapper extends IndexDeletionPolicy {
     }
   }
 
-
   /**
    * Internal use for Lucene... do not explicitly call.
    */
@@ -185,7 +191,8 @@ public final class IndexDeletionPolicyWrapper extends IndexDeletionPolicy {
       Long gen = delegate.getGeneration();
       Long reserve = reserves.get(gen);
       if (reserve != null && System.nanoTime() < reserve) return;
-      if(savedCommits.containsKey(gen)) return;
+      if (savedCommits.containsKey(gen)) return;
+      if (snapshotMgr.isSnapshotted(gen)) return;
       delegate.delete();
     }
 

solr/core/src/java/org/apache/solr/core/SolrConfig.java

@@ -28,7 +28,17 @@ import java.net.URL;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 import java.nio.file.Paths;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Properties;
+import java.util.Set;
+import java.util.UUID;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -49,6 +59,7 @@ import org.apache.solr.schema.IndexSchemaFactory;
 import org.apache.solr.search.CacheConfig;
 import org.apache.solr.search.FastLRUCache;
 import org.apache.solr.search.QParserPlugin;
+import org.apache.solr.search.SolrCache;
 import org.apache.solr.search.ValueSourceParser;
 import org.apache.solr.search.stats.StatsCache;
 import org.apache.solr.servlet.SolrRequestParsers;
@@ -91,7 +102,7 @@ public class SolrConfig extends Config implements MapSerializable {
   public static final String DEFAULT_CONF_FILE = "solrconfig.xml";
   private RequestParams requestParams;
 
-  public static enum PluginOpts {
+  public enum PluginOpts {
     MULTI_OK,
     REQUIRE_NAME,
     REQUIRE_NAME_IN_OVERLAY,
@@ -254,7 +265,6 @@ public class SolrConfig extends Config implements MapSerializable {
     dataDir = get("dataDir", null);
     if (dataDir != null && dataDir.length() == 0) dataDir = null;
 
-    userCacheConfigs = CacheConfig.getMultipleConfigs(this, "query/cache");
 
     org.apache.solr.search.SolrIndexSearcher.initRegenerators(this);
 
@@ -276,6 +286,16 @@ public class SolrConfig extends Config implements MapSerializable {
     maxWarmingSearchers = getInt("query/maxWarmingSearchers", Integer.MAX_VALUE);
     slowQueryThresholdMillis = getInt("query/slowQueryThresholdMillis", -1);
     for (SolrPluginInfo plugin : plugins) loadPluginInfo(plugin);
+
+    Map<String, CacheConfig> userCacheConfigs = CacheConfig.getMultipleConfigs(this, "query/cache");
+    List<PluginInfo> caches = getPluginInfos(SolrCache.class.getName());
+    if (!caches.isEmpty()) {
+      for (PluginInfo c : caches) {
+        userCacheConfigs.put(c.name, CacheConfig.getConfig(this, "cache", c.attributes, null));
+      }
+    }
+    this.userCacheConfigs = Collections.unmodifiableMap(userCacheConfigs);
+
     updateHandlerInfo = loadUpdatehandlerInfo();
 
     multipartUploadLimitKB = getInt(
@@ -317,6 +337,7 @@ public class SolrConfig extends Config implements MapSerializable {
       .add(new SolrPluginInfo(TransformerFactory.class, "transformer", REQUIRE_NAME, REQUIRE_CLASS, MULTI_OK))
       .add(new SolrPluginInfo(SearchComponent.class, "searchComponent", REQUIRE_NAME, REQUIRE_CLASS, MULTI_OK))
       .add(new SolrPluginInfo(UpdateRequestProcessorFactory.class, "updateProcessor", REQUIRE_NAME, REQUIRE_CLASS, MULTI_OK))
+      .add(new SolrPluginInfo(SolrCache.class, "cache", REQUIRE_NAME, REQUIRE_CLASS, MULTI_OK))
           // TODO: WTF is up with queryConverter???
           // it apparently *only* works as a singleton? - SOLR-4304
           // and even then -- only if there is a single SpellCheckComponent
@@ -457,7 +478,7 @@ public class SolrConfig extends Config implements MapSerializable {
   public final CacheConfig queryResultCacheConfig;
   public final CacheConfig documentCacheConfig;
   public final CacheConfig fieldValueCacheConfig;
-  public final CacheConfig[] userCacheConfigs;
+  public final Map<String, CacheConfig> userCacheConfigs;
   // SolrIndexSearcher - more...
   public final boolean useFilterForSortedQuery;
   public final int queryResultWindowSize;

solr/core/src/java/org/apache/solr/core/SolrCore.java

@@ -81,6 +81,7 @@ import org.apache.solr.common.util.ObjectReleaseTracker;
 import org.apache.solr.common.util.SimpleOrderedMap;
 import org.apache.solr.common.util.Utils;
 import org.apache.solr.core.DirectoryFactory.DirContext;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager;
 import org.apache.solr.handler.IndexFetcher;
 import org.apache.solr.handler.ReplicationHandler;
 import org.apache.solr.handler.RequestHandlerBase;
@@ -184,6 +185,7 @@ public final class SolrCore implements SolrInfoMBean, Closeable {
   private final Map<String,UpdateRequestProcessorChain> updateProcessorChains;
   private final Map<String, SolrInfoMBean> infoRegistry;
   private final IndexDeletionPolicyWrapper solrDelPolicy;
+  private final SolrSnapshotMetaDataManager snapshotMgr;
   private final DirectoryFactory directoryFactory;
   private IndexReaderFactory indexReaderFactory;
   private final Codec codec;
@@ -414,7 +416,19 @@ public final class SolrCore implements SolrInfoMBean, Closeable {
     } else {
       delPolicy = new SolrDeletionPolicy();
     }
-    return new IndexDeletionPolicyWrapper(delPolicy);
+
+    return new IndexDeletionPolicyWrapper(delPolicy, snapshotMgr);
+  }
+
+  private SolrSnapshotMetaDataManager initSnapshotMetaDataManager() {
+    try {
+      String dirName = getDataDir() + SolrSnapshotMetaDataManager.SNAPSHOT_METADATA_DIR + "/";
+      Directory snapshotDir = directoryFactory.get(dirName, DirContext.DEFAULT,
+           getSolrConfig().indexConfig.lockType);
+      return new SolrSnapshotMetaDataManager(this, snapshotDir);
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
   }
 
   private void initListeners() {
@@ -739,6 +753,7 @@ public final class SolrCore implements SolrInfoMBean, Closeable {
 
       initListeners();
 
+      this.snapshotMgr = initSnapshotMetaDataManager();
       this.solrDelPolicy = initDeletionPolicy(delPolicy);
 
       this.codec = initCodec(solrConfig, this.schema);
@@ -1242,6 +1257,17 @@ public final class SolrCore implements SolrInfoMBean, Closeable {
       }
     }
 
+    // Close the snapshots meta-data directory.
+    Directory snapshotsDir = snapshotMgr.getSnapshotsDir();
+    try {
+      this.directoryFactory.release(snapshotsDir);
+    }  catch (Throwable e) {
+      SolrException.log(log,e);
+      if (e instanceof Error) {
+        throw (Error) e;
+      }
+    }
+
     if (coreStateClosed) {
 
       try {
@@ -2343,6 +2369,14 @@ public final class SolrCore implements SolrInfoMBean, Closeable {
     return solrDelPolicy;
   }
 
+  /**
+   * @return A reference of {@linkplain SolrSnapshotMetaDataManager}
+   *         managing the persistent snapshots for this Solr core.
+   */
+  public SolrSnapshotMetaDataManager getSnapshotMetaDataManager() {
+    return snapshotMgr;
+  }
+
   public ReentrantLock getRuleExpiryLock() {
     return ruleExpiryLock;
   }

solr/core/src/java/org/apache/solr/core/backup/repository/LocalFileSystemRepository.java

@@ -32,6 +32,7 @@ import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.store.NoLockFactory;
 import org.apache.lucene.store.SimpleFSDirectory;
+import org.apache.lucene.util.Constants;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.core.DirectoryFactory;
 
@@ -59,10 +60,22 @@ public class LocalFileSystemRepository implements BackupRepository {
   @Override
   public URI createURI(String... pathComponents) {
     Preconditions.checkArgument(pathComponents.length > 0);
-    Path result = Paths.get(pathComponents[0]);
+
+    String basePath = Preconditions.checkNotNull(pathComponents[0]);
+    // Note the URI.getPath() invocation on Windows platform generates an invalid URI.
+    // Refer to http://stackoverflow.com/questions/9834776/java-nio-file-path-issue
+    // Since the caller may have used this method to generate the string representation
+    // for the pathComponents, we implement a work-around specifically for Windows platform
+    // to remove the leading '/' character.
+    if (Constants.WINDOWS) {
+      basePath = basePath.replaceFirst("^/(.:/)", "$1");
+    }
+
+    Path result = Paths.get(basePath);
     for (int i = 1; i < pathComponents.length; i++) {
       result = result.resolve(pathComponents[i]);
     }
+
     return result.toUri();
   }
 

solr/core/src/java/org/apache/solr/core/snapshots/SolrSnapshotManager.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.solr.core.snapshots;
+
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import com.google.common.annotations.VisibleForTesting;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexCommit;
+import org.apache.lucene.store.Directory;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager.SnapshotMetaData;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This class provides functionality required to handle the data files corresponding to Solr snapshots.
+ */
+public class SolrSnapshotManager {
+  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+
+  /**
+   * This method deletes index files of the {@linkplain IndexCommit} for the specified generation number.
+   *
+   * @param dir The index directory storing the snapshot.
+   * @param gen The generation number for the {@linkplain IndexCommit}
+   * @throws IOException in case of I/O errors.
+   */
+  public static void deleteIndexFiles ( Directory dir, Collection<SnapshotMetaData> snapshots, long gen ) throws IOException {
+    List<IndexCommit> commits = DirectoryReader.listCommits(dir);
+    Map<String, Integer> refCounts = buildRefCounts(snapshots, commits);
+    for (IndexCommit ic : commits) {
+      if (ic.getGeneration() == gen) {
+        deleteIndexFiles(dir,refCounts, ic);
+        break;
+      }
+    }
+  }
+
+  /**
+   * This method deletes all files not corresponding to a configured snapshot in the specified index directory.
+   *
+   * @param dir The index directory to search for.
+   * @throws IOException in case of I/O errors.
+   */
+  public static void deleteNonSnapshotIndexFiles (Directory dir, Collection<SnapshotMetaData> snapshots) throws IOException {
+    List<IndexCommit> commits = DirectoryReader.listCommits(dir);
+    Map<String, Integer> refCounts = buildRefCounts(snapshots, commits);
+    Set<Long> snapshotGenNumbers = snapshots.stream()
+                                            .map(SnapshotMetaData::getGenerationNumber)
+                                            .collect(Collectors.toSet());
+    for (IndexCommit ic : commits) {
+      if (!snapshotGenNumbers.contains(ic.getGeneration())) {
+        deleteIndexFiles(dir,refCounts, ic);
+      }
+    }
+  }
+
+  /**
+   * This method computes reference count for the index files by taking into consideration
+   * (a) configured snapshots and (b) files sharing between two or more {@linkplain IndexCommit} instances.
+   *
+   * @param snapshots A collection of user configured snapshots
+   * @param commits A list of {@linkplain IndexCommit} instances
+   * @return A map containing reference count for each index file referred in one of the {@linkplain IndexCommit} instances.
+   * @throws IOException in case of I/O error.
+   */
+  @VisibleForTesting
+  static Map<String, Integer> buildRefCounts (Collection<SnapshotMetaData> snapshots, List<IndexCommit> commits) throws IOException {
+    Map<String, Integer> result = new HashMap<>();
+    Map<Long, IndexCommit> commitsByGen = commits.stream().collect(
+        Collectors.toMap(IndexCommit::getGeneration, Function.identity()));
+
+    for(SnapshotMetaData md : snapshots) {
+      IndexCommit ic = commitsByGen.get(md.getGenerationNumber());
+      if (ic != null) {
+        Collection<String> fileNames = ic.getFileNames();
+        for(String fileName : fileNames) {
+          int refCount = result.getOrDefault(fileName, 0);
+          result.put(fileName, refCount+1);
+        }
+      }
+    }
+
+    return result;
+  }
+
+  /**
+   * This method deletes the index files associated with specified <code>indexCommit</code> provided they
+   * are not referred by some other {@linkplain IndexCommit}.
+   *
+   * @param dir The index directory containing the {@linkplain IndexCommit} to be deleted.
+   * @param refCounts A map containing reference counts for each file associated with every {@linkplain IndexCommit}
+   *                  in the specified directory.
+   * @param indexCommit The {@linkplain IndexCommit} whose files need to be deleted.
+   * @throws IOException in case of I/O errors.
+   */
+  private static void deleteIndexFiles ( Directory dir, Map<String, Integer> refCounts, IndexCommit indexCommit ) throws IOException {
+    log.info("Deleting index files for index commit with generation {} in directory {}", indexCommit.getGeneration(), dir);
+    for (String fileName : indexCommit.getFileNames()) {
+      try {
+        // Ensure that a file being deleted is not referred by some other commit.
+        int ref = refCounts.getOrDefault(fileName, 0);
+        log.debug("Reference count for file {} is {}", fileName, ref);
+        if (ref == 0) {
+          dir.deleteFile(fileName);
+        }
+      } catch (IOException e) {
+        log.warn("Unable to delete file {} in directory {} due to exception {}", fileName, dir, e.getMessage());
+      }
+    }
+  }
+}

solr/core/src/java/org/apache/solr/core/snapshots/SolrSnapshotMetaDataManager.java

@@ -0,0 +1,416 @@
+/*
+ * 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.solr.core.snapshots;
+
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+import com.google.common.base.Preconditions;
+import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexCommit;
+import org.apache.lucene.index.IndexDeletionPolicy;
+import org.apache.lucene.index.IndexWriterConfig.OpenMode;
+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.util.IOUtils;
+import org.apache.solr.common.SolrException;
+import org.apache.solr.common.SolrException.ErrorCode;
+import org.apache.solr.core.DirectoryFactory;
+import org.apache.solr.core.DirectoryFactory.DirContext;
+import org.apache.solr.core.IndexDeletionPolicyWrapper;
+import org.apache.solr.core.SolrCore;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This class is responsible to manage the persistent snapshots meta-data for the Solr indexes. The
+ * persistent snapshots are implemented by relying on Lucene {@linkplain IndexDeletionPolicy}
+ * abstraction to configure a specific {@linkplain IndexCommit} to be retained. The
+ * {@linkplain IndexDeletionPolicyWrapper} in Solr uses this class to create/delete the Solr index
+ * snapshots.
+ */
+public class SolrSnapshotMetaDataManager {
+  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+  public static final String SNAPSHOT_METADATA_DIR = "snapshot_metadata";
+
+  /**
+   * A class defining the meta-data for a specific snapshot.
+   */
+  public static class SnapshotMetaData {
+    private String name;
+    private String indexDirPath;
+    private long generationNumber;
+
+    public SnapshotMetaData(String name, String indexDirPath, long generationNumber) {
+      super();
+      this.name = name;
+      this.indexDirPath = indexDirPath;
+      this.generationNumber = generationNumber;
+    }
+
+    public String getName() {
+      return name;
+    }
+
+    public String getIndexDirPath() {
+      return indexDirPath;
+    }
+
+    public long getGenerationNumber() {
+      return generationNumber;
+    }
+
+    @Override
+    public String toString() {
+      StringBuilder builder = new StringBuilder();
+      builder.append("SnapshotMetaData[name=");
+      builder.append(name);
+      builder.append(", indexDirPath=");
+      builder.append(indexDirPath);
+      builder.append(", generation=");
+      builder.append(generationNumber);
+      builder.append("]");
+      return builder.toString();
+    }
+  }
+
+  /** Prefix used for the save file. */
+  public static final String SNAPSHOTS_PREFIX = "snapshots_";
+  private static final int VERSION_START = 0;
+  private static final int VERSION_CURRENT = VERSION_START;
+  private static final String CODEC_NAME = "solr-snapshots";
+
+  // The index writer which maintains the snapshots metadata
+  private long nextWriteGen;
+
+  private final Directory dir;
+
+  /** Used to map snapshot name to snapshot meta-data. */
+  protected final Map<String,SnapshotMetaData> nameToDetailsMapping = new LinkedHashMap<>();
+  /** Used to figure out the *current* index data directory path */
+  private final SolrCore solrCore;
+
+  /**
+   * A constructor.
+   *
+   * @param dir The directory where the snapshot meta-data should be stored. Enables updating
+   *            the existing meta-data.
+   * @throws IOException in case of errors.
+   */
+  public SolrSnapshotMetaDataManager(SolrCore solrCore, Directory dir) throws IOException {
+    this(solrCore, dir, OpenMode.CREATE_OR_APPEND);
+  }
+
+  /**
+   * A constructor.
+   *
+   * @param dir The directory where the snapshot meta-data is stored.
+   * @param mode CREATE If previous meta-data should be erased.
+   *             APPEND If previous meta-data should be read and updated.
+   *             CREATE_OR_APPEND Creates a new meta-data structure if one does not exist
+   *                              Updates the existing structure if one exists.
+   * @throws IOException in case of errors.
+   */
+  public SolrSnapshotMetaDataManager(SolrCore solrCore, Directory dir, OpenMode mode) throws IOException {
+    this.solrCore = solrCore;
+    this.dir = dir;
+
+    if (mode == OpenMode.CREATE) {
+      deleteSnapshotMetadataFiles();
+    }
+
+    loadFromSnapshotMetadataFile();
+
+    if (mode == OpenMode.APPEND && nextWriteGen == 0) {
+      throw new IllegalStateException("no snapshots stored in this directory");
+    }
+  }
+
+  /**
+   * @return The snapshot meta-data directory
+   */
+  public Directory getSnapshotsDir() {
+    return dir;
+  }
+
+  /**
+   * This method creates a new snapshot meta-data entry.
+   *
+   * @param name The name of the snapshot.
+   * @param indexDirPath The directory path where the index files are stored.
+   * @param gen The generation number for the {@linkplain IndexCommit} being snapshotted.
+   * @throws IOException in case of I/O errors.
+   */
+  public synchronized void snapshot(String name, String indexDirPath, long gen) throws IOException {
+    Preconditions.checkNotNull(name);
+
+    log.info("Creating the snapshot named {} for core {} associated with index commit with generation {} in directory {}"
+        , name, solrCore.getName(), gen, indexDirPath);
+
+    if(nameToDetailsMapping.containsKey(name)) {
+      throw new SolrException(ErrorCode.BAD_REQUEST, "A snapshot with name " + name + " already exists");
+    }
+
+    SnapshotMetaData d = new SnapshotMetaData(name, indexDirPath, gen);
+    nameToDetailsMapping.put(name, d);
+
+    boolean success = false;
+    try {
+      persist();
+      success = true;
+    } finally {
+      if (!success) {
+        try {
+          release(name);
+        } catch (Exception e) {
+          // Suppress so we keep throwing original exception
+        }
+      }
+    }
+  }
+
+  /**
+   * This method deletes a previously created snapshot (if any).
+   *
+   * @param name The name of the snapshot to be deleted.
+   * @return The snapshot meta-data if the snapshot with the snapshot name exists.
+   * @throws IOException in case of I/O error
+   */
+  public synchronized Optional<SnapshotMetaData> release(String name) throws IOException {
+    log.info("Deleting the snapshot named {} for core {}", name, solrCore.getName());
+    SnapshotMetaData result = nameToDetailsMapping.remove(Preconditions.checkNotNull(name));
+    if(result != null) {
+      boolean success = false;
+      try {
+        persist();
+        success = true;
+      } finally {
+        if (!success) {
+          nameToDetailsMapping.put(name, result);
+        }
+      }
+    }
+    return Optional.ofNullable(result);
+  }
+
+  /**
+   * This method returns if snapshot is created for the specified generation number in
+   * the *current* index directory.
+   *
+   * @param genNumber The generation number for the {@linkplain IndexCommit} to be checked.
+   * @return true if the snapshot is created.
+   *         false otherwise.
+   */
+  public synchronized boolean isSnapshotted(long genNumber) {
+    return !nameToDetailsMapping.isEmpty() && isSnapshotted(solrCore.getIndexDir(), genNumber);
+  }
+
+  /**
+   * This method returns if snapshot is created for the specified generation number in
+   * the specified index directory.
+   *
+   * @param genNumber The generation number for the {@linkplain IndexCommit} to be checked.
+   * @return true if the snapshot is created.
+   *         false otherwise.
+   */
+  public synchronized boolean isSnapshotted(String indexDirPath, long genNumber) {
+    return !nameToDetailsMapping.isEmpty()
+        && nameToDetailsMapping.values().stream()
+           .anyMatch(entry -> entry.getIndexDirPath().equals(indexDirPath) && entry.getGenerationNumber() == genNumber);
+  }
+
+  /**
+   * This method returns the snapshot meta-data for the specified name (if it exists).
+   *
+   * @param name The name of the snapshot
+   * @return The snapshot meta-data if exists.
+   */
+  public synchronized Optional<SnapshotMetaData> getSnapshotMetaData(String name) {
+    return Optional.ofNullable(nameToDetailsMapping.get(name));
+  }
+
+  /**
+   * @return A list of snapshots created so far.
+   */
+  public synchronized List<String> listSnapshots() {
+    // We create a copy for thread safety.
+    return new ArrayList<>(nameToDetailsMapping.keySet());
+  }
+
+  /**
+   * This method returns a list of snapshots created in a specified index directory.
+   *
+   * @param indexDirPath The index directory path.
+   * @return a list snapshots stored in the specified directory.
+   */
+  public synchronized Collection<SnapshotMetaData> listSnapshotsInIndexDir(String indexDirPath) {
+    return nameToDetailsMapping.values().stream()
+        .filter(entry -> indexDirPath.equals(entry.getIndexDirPath()))
+        .collect(Collectors.toList());
+  }
+
+  /**
+   * This method returns the {@linkplain IndexCommit} associated with the specified
+   * <code>commitName</code>. A snapshot with specified <code>commitName</code> must
+   * be created before invoking this method.
+   *
+   * @param commitName The name of persisted commit
+   * @return the {@linkplain IndexCommit}
+   * @throws IOException in case of I/O error.
+   */
+  public Optional<IndexCommit> getIndexCommitByName(String commitName) throws IOException {
+    Optional<IndexCommit> result = Optional.empty();
+    Optional<SnapshotMetaData> metaData = getSnapshotMetaData(commitName);
+    if (metaData.isPresent()) {
+      String indexDirPath = metaData.get().getIndexDirPath();
+      long gen = metaData.get().getGenerationNumber();
+
+      Directory d = solrCore.getDirectoryFactory().get(indexDirPath, DirContext.DEFAULT, DirectoryFactory.LOCK_TYPE_NONE);
+      try {
+        result = DirectoryReader.listCommits(d)
+                                .stream()
+                                .filter(ic -> ic.getGeneration() == gen)
+                                .findAny();
+
+        if (!result.isPresent()) {
+          log.warn("Unable to find commit with generation {} in the directory {}", gen, indexDirPath);
+        }
+
+      } finally {
+        solrCore.getDirectoryFactory().release(d);
+      }
+    } else {
+      log.warn("Commit with name {} is not persisted for core {}", commitName, solrCore.getName());
+    }
+
+    return result;
+  }
+
+  private synchronized void persist() throws IOException {
+    String fileName = SNAPSHOTS_PREFIX + nextWriteGen;
+    IndexOutput out = dir.createOutput(fileName, IOContext.DEFAULT);
+    boolean success = false;
+    try {
+      CodecUtil.writeHeader(out, CODEC_NAME, VERSION_CURRENT);
+      out.writeVInt(nameToDetailsMapping.size());
+      for(Entry<String,SnapshotMetaData> ent : nameToDetailsMapping.entrySet()) {
+        out.writeString(ent.getKey());
+        out.writeString(ent.getValue().getIndexDirPath());
+        out.writeVLong(ent.getValue().getGenerationNumber());
+      }
+      success = true;
+    } finally {
+      if (!success) {
+        IOUtils.closeWhileHandlingException(out);
+        IOUtils.deleteFilesIgnoringExceptions(dir, fileName);
+      } else {
+        IOUtils.close(out);
+      }
+    }
+
+    dir.sync(Collections.singletonList(fileName));
+
+    if (nextWriteGen > 0) {
+      String lastSaveFile = SNAPSHOTS_PREFIX + (nextWriteGen-1);
+      // exception OK: likely it didn't exist
+      IOUtils.deleteFilesIgnoringExceptions(dir, lastSaveFile);
+    }
+
+    nextWriteGen++;
+  }
+
+  private synchronized void deleteSnapshotMetadataFiles() throws IOException {
+    for(String file : dir.listAll()) {
+      if (file.startsWith(SNAPSHOTS_PREFIX)) {
+        dir.deleteFile(file);
+      }
+    }
+  }
+
+  /**
+   * Reads the snapshot meta-data information from the given {@link Directory}.
+   */
+  private synchronized void loadFromSnapshotMetadataFile() throws IOException {
+    log.info("Loading from snapshot metadata file...");
+    long genLoaded = -1;
+    IOException ioe = null;
+    List<String> snapshotFiles = new ArrayList<>();
+    for(String file : dir.listAll()) {
+      if (file.startsWith(SNAPSHOTS_PREFIX)) {
+        long gen = Long.parseLong(file.substring(SNAPSHOTS_PREFIX.length()));
+        if (genLoaded == -1 || gen > genLoaded) {
+          snapshotFiles.add(file);
+          Map<String, SnapshotMetaData> snapshotMetaDataMapping = new HashMap<>();
+          IndexInput in = dir.openInput(file, IOContext.DEFAULT);
+          try {
+            CodecUtil.checkHeader(in, CODEC_NAME, VERSION_START, VERSION_START);
+            int count = in.readVInt();
+            for(int i=0;i<count;i++) {
+              String name = in.readString();
+              String indexDirPath = in.readString();
+              long commitGen = in.readVLong();
+              snapshotMetaDataMapping.put(name, new SnapshotMetaData(name, indexDirPath, commitGen));
+            }
+          } catch (IOException ioe2) {
+            // Save first exception & throw in the end
+            if (ioe == null) {
+              ioe = ioe2;
+            }
+          } finally {
+            in.close();
+          }
+
+          genLoaded = gen;
+          nameToDetailsMapping.clear();
+          nameToDetailsMapping.putAll(snapshotMetaDataMapping);
+        }
+      }
+    }
+
+    if (genLoaded == -1) {
+      // Nothing was loaded...
+      if (ioe != null) {
+        // ... not for lack of trying:
+        throw ioe;
+      }
+    } else {
+      if (snapshotFiles.size() > 1) {
+        // Remove any broken / old snapshot files:
+        String curFileName = SNAPSHOTS_PREFIX + genLoaded;
+        for(String file : snapshotFiles) {
+          if (!curFileName.equals(file)) {
+            IOUtils.deleteFilesIgnoringExceptions(dir, file);
+          }
+        }
+      }
+      nextWriteGen = 1+genLoaded;
+    }
+  }
+}

solr/core/src/java/org/apache/solr/core/snapshots/package-info.java

@@ -0,0 +1,22 @@
+/*
+* 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.
+*/
+
+
+/**
+ * Core classes for Solr's persistent snapshots functionality
+ */
+package org.apache.solr.core.snapshots;

solr/core/src/java/org/apache/solr/handler/BlobHandler.java

@@ -160,7 +160,7 @@ public class BlobHandler extends RequestHandlerBase implements PluginInfoInitial
         } else {
           String q = "blobName:{0}";
           if (version != -1) q = "id:{0}/{1}";
-          QParser qparser = QParser.getParser(StrUtils.formatString(q, blobName, version), "lucene", req);
+          QParser qparser = QParser.getParser(StrUtils.formatString(q, blobName, version), req);
           final TopDocs docs = req.getSearcher().search(qparser.parse(), 1, new Sort(new SortField("version", SortField.Type.LONG, true)));
           if (docs.totalHits > 0) {
             rsp.add(ReplicationHandler.FILE_STREAM, new SolrCore.RawWriter() {

solr/core/src/java/org/apache/solr/handler/CdcrParams.java

@@ -121,6 +121,11 @@ public class CdcrParams {
    */
   public final static String COUNTER_DELETES = "deletes";
 
+  /**
+   * Counter for Bootstrap operations *
+   */
+  public final static String COUNTER_BOOTSTRAP = "bootstraps";
+
   /**
    * A list of errors per target collection *
    */
@@ -165,7 +170,10 @@ public class CdcrParams {
     LASTPROCESSEDVERSION,
     QUEUES,
     OPS,
-    ERRORS;
+    ERRORS,
+    BOOTSTRAP,
+    BOOTSTRAP_STATUS,
+    CANCEL_BOOTSTRAP;
 
     public static CdcrAction get(String p) {
       if (p != null) {

solr/core/src/java/org/apache/solr/handler/CdcrReplicator.java

@@ -119,7 +119,7 @@ public class CdcrReplicator implements Runnable {
       // we might have read a single commit operation and reached the end of the update logs
       logReader.forwardSeek(subReader);
 
-      log.debug("Forwarded {} updates to target {}", counter, state.getTargetCollection());
+      log.info("Forwarded {} updates to target {}", counter, state.getTargetCollection());
     } catch (Exception e) {
       // report error and update error stats
       this.handleException(e);
@@ -150,13 +150,13 @@ public class CdcrReplicator implements Runnable {
     if (e instanceof CdcrReplicatorException) {
       UpdateRequest req = ((CdcrReplicatorException) e).req;
       UpdateResponse rsp = ((CdcrReplicatorException) e).rsp;
-      log.warn("Failed to forward update request {}. Got response {}", req, rsp);
+      log.warn("Failed to forward update request {} to target: {}. Got response {}", req, state.getTargetCollection(), rsp);
       state.reportError(CdcrReplicatorState.ErrorType.BAD_REQUEST);
     } else if (e instanceof CloudSolrClient.RouteException) {
-      log.warn("Failed to forward update request", e);
+      log.warn("Failed to forward update request to target: " + state.getTargetCollection(), e);
       state.reportError(CdcrReplicatorState.ErrorType.BAD_REQUEST);
     } else {
-      log.warn("Failed to forward update request", e);
+      log.warn("Failed to forward update request to target: " + state.getTargetCollection(), e);
       state.reportError(CdcrReplicatorState.ErrorType.INTERNAL);
     }
   }

solr/core/src/java/org/apache/solr/handler/CdcrReplicatorManager.java

@@ -16,29 +16,49 @@
  */
 package org.apache.solr.handler;
 
+import java.io.Closeable;
 import java.io.IOException;
 import java.lang.invoke.MethodHandles;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.TimeUnit;
 
+import org.apache.http.client.HttpClient;
+import org.apache.solr.client.solrj.SolrClient;
 import org.apache.solr.client.solrj.SolrRequest;
 import org.apache.solr.client.solrj.SolrServerException;
 import org.apache.solr.client.solrj.impl.CloudSolrClient;
 import org.apache.solr.client.solrj.impl.CloudSolrClient.Builder;
+import org.apache.solr.client.solrj.impl.HttpSolrClient;
 import org.apache.solr.client.solrj.request.QueryRequest;
 import org.apache.solr.common.SolrException;
+import org.apache.solr.common.cloud.Replica;
+import org.apache.solr.common.cloud.ZkCoreNodeProps;
 import org.apache.solr.common.params.CommonParams;
 import org.apache.solr.common.params.ModifiableSolrParams;
 import org.apache.solr.common.params.SolrParams;
+import org.apache.solr.common.util.ExecutorUtil;
+import org.apache.solr.common.util.IOUtils;
 import org.apache.solr.common.util.NamedList;
+import org.apache.solr.common.util.SolrjNamedThreadFactory;
 import org.apache.solr.core.SolrCore;
 import org.apache.solr.update.CdcrUpdateLog;
+import org.apache.solr.util.TimeOut;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import static org.apache.solr.handler.admin.CoreAdminHandler.RESPONSE_STATUS;
+
 class CdcrReplicatorManager implements CdcrStateManager.CdcrStateObserver {
 
+  private static final int MAX_BOOTSTRAP_ATTEMPTS = 5;
+  private static final int BOOTSTRAP_RETRY_DELAY_MS = 2000;
+  // 6 hours is hopefully long enough for most indexes
+  private static final long BOOTSTRAP_TIMEOUT_SECONDS = 6L * 3600L * 3600L;
+
   private List<CdcrReplicatorState> replicatorStates;
 
   private final CdcrReplicatorScheduler scheduler;
@@ -48,6 +68,9 @@ class CdcrReplicatorManager implements CdcrStateManager.CdcrStateObserver {
   private SolrCore core;
   private String path;
 
+  private ExecutorService bootstrapExecutor;
+  private volatile BootstrapStatusRunnable bootstrapStatusRunnable;
+
   private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
 
   CdcrReplicatorManager(final SolrCore core, String path,
@@ -104,12 +127,20 @@ class CdcrReplicatorManager implements CdcrStateManager.CdcrStateObserver {
   @Override
   public synchronized void stateUpdate() {
     if (leaderStateManager.amILeader() && processStateManager.getState().equals(CdcrParams.ProcessState.STARTED)) {
+      if (replicatorStates.size() > 0)  {
+        this.bootstrapExecutor = ExecutorUtil.newMDCAwareFixedThreadPool(replicatorStates.size(),
+            new SolrjNamedThreadFactory("cdcr-bootstrap-status"));
+      }
       this.initLogReaders();
       this.scheduler.start();
       return;
     }
 
     this.scheduler.shutdown();
+    if (bootstrapExecutor != null)  {
+      IOUtils.closeQuietly(bootstrapStatusRunnable);
+      ExecutorUtil.shutdownAndAwaitTermination(bootstrapExecutor);
+    }
     this.closeLogReaders();
   }
 
@@ -117,7 +148,7 @@ class CdcrReplicatorManager implements CdcrStateManager.CdcrStateObserver {
     return replicatorStates;
   }
 
-  void initLogReaders() {
+  private void initLogReaders() {
     String collectionName = core.getCoreDescriptor().getCloudDescriptor().getCollectionName();
     String shard = core.getCoreDescriptor().getCloudDescriptor().getShardId();
     CdcrUpdateLog ulog = (CdcrUpdateLog) core.getUpdateHandler().getUpdateLog();
@@ -129,8 +160,23 @@ class CdcrReplicatorManager implements CdcrStateManager.CdcrStateObserver {
         log.info("Create new update log reader for target {} with checkpoint {} @ {}:{}", state.getTargetCollection(),
             checkpoint, collectionName, shard);
         CdcrUpdateLog.CdcrLogReader reader = ulog.newLogReader();
-        reader.seek(checkpoint);
+        boolean seek = reader.seek(checkpoint);
         state.init(reader);
+        if (!seek) {
+          // targetVersion is lower than the oldest known entry.
+          // In this scenario, it probably means that there is a gap in the updates log.
+          // the best we can do here is to bootstrap the target leader by replicating the full index
+          final String targetCollection = state.getTargetCollection();
+          state.setBootstrapInProgress(true);
+          log.info("Attempting to bootstrap target collection: {}, shard: {}", targetCollection, shard);
+          bootstrapStatusRunnable = new BootstrapStatusRunnable(core, state);
+          log.info("Submitting bootstrap task to executor");
+          try {
+            bootstrapExecutor.submit(bootstrapStatusRunnable);
+          } catch (Exception e) {
+            log.error("Unable to submit bootstrap call to executor", e);
+          }
+        }
       } catch (IOException | SolrServerException | SolrException e) {
         log.warn("Unable to instantiate the log reader for target collection " + state.getTargetCollection(), e);
       } catch (InterruptedException e) {
@@ -164,11 +210,203 @@ class CdcrReplicatorManager implements CdcrStateManager.CdcrStateObserver {
    */
   void shutdown() {
     this.scheduler.shutdown();
+    if (bootstrapExecutor != null)  {
+      IOUtils.closeQuietly(bootstrapStatusRunnable);
+      ExecutorUtil.shutdownAndAwaitTermination(bootstrapExecutor);
+    }
     for (CdcrReplicatorState state : replicatorStates) {
       state.shutdown();
     }
     replicatorStates.clear();
   }
 
+  private class BootstrapStatusRunnable implements Runnable, Closeable {
+    private final CdcrReplicatorState state;
+    private final String targetCollection;
+    private final String shard;
+    private final String collectionName;
+    private final CdcrUpdateLog ulog;
+    private final String myCoreUrl;
+
+    private volatile boolean closed = false;
+
+    BootstrapStatusRunnable(SolrCore core, CdcrReplicatorState state) {
+      this.collectionName = core.getCoreDescriptor().getCloudDescriptor().getCollectionName();
+      this.shard = core.getCoreDescriptor().getCloudDescriptor().getShardId();
+      this.ulog = (CdcrUpdateLog) core.getUpdateHandler().getUpdateLog();
+      this.state = state;
+      this.targetCollection = state.getTargetCollection();
+      String baseUrl = core.getCoreDescriptor().getCoreContainer().getZkController().getBaseUrl();
+      this.myCoreUrl = ZkCoreNodeProps.getCoreUrl(baseUrl, core.getName());
+    }
+
+    @Override
+    public void close() throws IOException {
+      closed = true;
+      try {
+        Replica leader = state.getClient().getZkStateReader().getLeaderRetry(targetCollection, shard, 30000); // assume same shard exists on target
+        String leaderCoreUrl = leader.getCoreUrl();
+        HttpClient httpClient = state.getClient().getLbClient().getHttpClient();
+        try (HttpSolrClient client = new HttpSolrClient.Builder(leaderCoreUrl).withHttpClient(httpClient).build()) {
+          sendCdcrCommand(client, CdcrParams.CdcrAction.CANCEL_BOOTSTRAP);
+        } catch (SolrServerException e) {
+          log.error("Error sending cancel bootstrap message to target collection: {} shard: {} leader: {}",
+              targetCollection, shard, leaderCoreUrl);
+        }
+      } catch (InterruptedException e) {
+        log.error("Interrupted while closing BootstrapStatusRunnable", e);
+        Thread.currentThread().interrupt();
+      }
+    }
+
+    @Override
+    public void run() {
+      int retries = 1;
+      boolean success = false;
+      try {
+        while (!closed && sendBootstrapCommand() != BootstrapStatus.SUBMITTED)  {
+          Thread.sleep(BOOTSTRAP_RETRY_DELAY_MS);
+        }
+        TimeOut timeOut = new TimeOut(BOOTSTRAP_TIMEOUT_SECONDS, TimeUnit.SECONDS);
+        while (!timeOut.hasTimedOut()) {
+          if (closed) {
+            log.warn("Cancelling waiting for bootstrap on target: {} shard: {} to complete", targetCollection, shard);
+            state.setBootstrapInProgress(false);
+            break;
+          }
+          BootstrapStatus status = getBoostrapStatus();
+          if (status == BootstrapStatus.RUNNING) {
+            try {
+              log.info("CDCR bootstrap running for {} seconds, sleeping for {} ms",
+                  BOOTSTRAP_TIMEOUT_SECONDS - timeOut.timeLeft(TimeUnit.SECONDS), BOOTSTRAP_RETRY_DELAY_MS);
+              Thread.sleep(BOOTSTRAP_RETRY_DELAY_MS);
+            } catch (InterruptedException e) {
+              Thread.currentThread().interrupt();
+            }
+          } else if (status == BootstrapStatus.COMPLETED) {
+            log.info("CDCR bootstrap successful in {} seconds", BOOTSTRAP_TIMEOUT_SECONDS - timeOut.timeLeft(TimeUnit.SECONDS));
+            long checkpoint = CdcrReplicatorManager.this.getCheckpoint(state);
+            log.info("Create new update log reader for target {} with checkpoint {} @ {}:{}", state.getTargetCollection(),
+                checkpoint, collectionName, shard);
+            CdcrUpdateLog.CdcrLogReader reader1 = ulog.newLogReader();
+            reader1.seek(checkpoint);
+            success = true;
+            break;
+          } else if (status == BootstrapStatus.FAILED) {
+            log.warn("CDCR bootstrap failed in {} seconds", BOOTSTRAP_TIMEOUT_SECONDS - timeOut.timeLeft(TimeUnit.SECONDS));
+            // let's retry a fixed number of times before giving up
+            if (retries >= MAX_BOOTSTRAP_ATTEMPTS) {
+              log.error("Unable to bootstrap the target collection: {}, shard: {} even after {} retries", targetCollection, shard, retries);
+              break;
+            } else {
+              log.info("Retry: {} - Attempting to bootstrap target collection: {} shard: {}", retries, targetCollection, shard);
+              while (!closed && sendBootstrapCommand() != BootstrapStatus.SUBMITTED)  {
+                Thread.sleep(BOOTSTRAP_RETRY_DELAY_MS);
+              }
+              timeOut = new TimeOut(BOOTSTRAP_TIMEOUT_SECONDS, TimeUnit.SECONDS); // reset the timer
+              retries++;
+            }
+          } else if (status == BootstrapStatus.NOTFOUND) {
+            // the leader of the target shard may have changed and therefore there is no record of the
+            // bootstrap process so we must retry the operation
+            while (!closed && sendBootstrapCommand() != BootstrapStatus.SUBMITTED)  {
+              Thread.sleep(BOOTSTRAP_RETRY_DELAY_MS);
+            }
+            retries = 1;
+            timeOut = new TimeOut(6L * 3600L * 3600L, TimeUnit.SECONDS); // reset the timer
+          } else if (status == BootstrapStatus.UNKNOWN) {
+            // we were not able to query the status on the remote end
+            // so just sleep for a bit and try again
+            Thread.sleep(BOOTSTRAP_RETRY_DELAY_MS);
+          }
+        }
+      } catch (InterruptedException e) {
+        log.info("Bootstrap thread interrupted");
+        state.reportError(CdcrReplicatorState.ErrorType.INTERNAL);
+        Thread.currentThread().interrupt();
+      } catch (IOException | SolrServerException | SolrException e) {
+        log.error("Unable to bootstrap the target collection " + targetCollection + " shard: " + shard, e);
+        state.reportError(CdcrReplicatorState.ErrorType.BAD_REQUEST);
+      } finally {
+        if (success) {
+          log.info("Bootstrap successful, giving the go-ahead to replicator");
+          state.setBootstrapInProgress(false);
+        }
+      }
+    }
+
+    private BootstrapStatus sendBootstrapCommand() throws InterruptedException {
+      Replica leader = state.getClient().getZkStateReader().getLeaderRetry(targetCollection, shard, 30000); // assume same shard exists on target
+      String leaderCoreUrl = leader.getCoreUrl();
+      HttpClient httpClient = state.getClient().getLbClient().getHttpClient();
+      try (HttpSolrClient client = new HttpSolrClient.Builder(leaderCoreUrl).withHttpClient(httpClient).build()) {
+        log.info("Attempting to bootstrap target collection: {} shard: {} leader: {}", targetCollection, shard, leaderCoreUrl);
+        try {
+          NamedList response = sendCdcrCommand(client, CdcrParams.CdcrAction.BOOTSTRAP, ReplicationHandler.MASTER_URL, myCoreUrl);
+          log.debug("CDCR Bootstrap response: {}", response);
+          String status = response.get(RESPONSE_STATUS).toString();
+          return BootstrapStatus.valueOf(status.toUpperCase(Locale.ROOT));
+        } catch (Exception e) {
+          log.error("Exception submitting bootstrap request", e);
+          return BootstrapStatus.UNKNOWN;
+        }
+      } catch (IOException e) {
+        log.error("There shouldn't be an IOException while closing but there was!", e);
+      }
+      return BootstrapStatus.UNKNOWN;
+    }
+
+    private BootstrapStatus getBoostrapStatus() throws InterruptedException {
+      try {
+        Replica leader = state.getClient().getZkStateReader().getLeaderRetry(targetCollection, shard, 30000); // assume same shard exists on target
+        String leaderCoreUrl = leader.getCoreUrl();
+        HttpClient httpClient = state.getClient().getLbClient().getHttpClient();
+        try (HttpSolrClient client = new HttpSolrClient.Builder(leaderCoreUrl).withHttpClient(httpClient).build()) {
+          NamedList response = sendCdcrCommand(client, CdcrParams.CdcrAction.BOOTSTRAP_STATUS);
+          String status = (String) response.get(RESPONSE_STATUS);
+          BootstrapStatus bootstrapStatus = BootstrapStatus.valueOf(status.toUpperCase(Locale.ROOT));
+          if (bootstrapStatus == BootstrapStatus.RUNNING) {
+            return BootstrapStatus.RUNNING;
+          } else if (bootstrapStatus == BootstrapStatus.COMPLETED) {
+            return BootstrapStatus.COMPLETED;
+          } else if (bootstrapStatus == BootstrapStatus.FAILED) {
+            return BootstrapStatus.FAILED;
+          } else if (bootstrapStatus == BootstrapStatus.NOTFOUND) {
+            log.warn("Bootstrap process was not found on target collection: {} shard: {}, leader: {}", targetCollection, shard, leaderCoreUrl);
+            return BootstrapStatus.NOTFOUND;
+          } else if (bootstrapStatus == BootstrapStatus.CANCELLED) {
+            return BootstrapStatus.CANCELLED;
+          } else {
+            throw new SolrException(SolrException.ErrorCode.SERVER_ERROR,
+                "Unknown status: " + status + " returned by BOOTSTRAP_STATUS command");
+          }
+        }
+      } catch (Exception e) {
+        log.error("Exception during bootstrap status request", e);
+        return BootstrapStatus.UNKNOWN;
+      }
+    }
+  }
+
+  private NamedList sendCdcrCommand(SolrClient client, CdcrParams.CdcrAction action, String... params) throws SolrServerException, IOException {
+    ModifiableSolrParams solrParams = new ModifiableSolrParams();
+    solrParams.set(CommonParams.QT, "/cdcr");
+    solrParams.set(CommonParams.ACTION, action.toString());
+    for (int i = 0; i < params.length - 1; i+=2) {
+      solrParams.set(params[i], params[i + 1]);
+    }
+    SolrRequest request = new QueryRequest(solrParams);
+    return client.request(request);
+  }
+
+  private enum BootstrapStatus  {
+    SUBMITTED,
+    RUNNING,
+    COMPLETED,
+    FAILED,
+    NOTFOUND,
+    CANCELLED,
+    UNKNOWN
+  }
 }
 

solr/core/src/java/org/apache/solr/handler/CdcrReplicatorScheduler.java

@@ -77,7 +77,11 @@ class CdcrReplicatorScheduler {
             CdcrReplicatorState state = statesQueue.poll();
             assert state != null; // Should never happen
             try {
+              if (!state.isBootstrapInProgress()) {
                 new CdcrReplicator(state, batchSize).run();
+              } else  {
+                log.debug("Replicator state is bootstrapping, skipping replication for target collection {}", state.getTargetCollection());
+              }
             } finally {
               statesQueue.offer(state);
             }

solr/core/src/java/org/apache/solr/handler/CdcrReplicatorState.java

@@ -27,6 +27,8 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import org.apache.solr.client.solrj.impl.CloudSolrClient;
 import org.apache.solr.update.CdcrUpdateLog;
@@ -53,6 +55,9 @@ class CdcrReplicatorState {
 
   private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
 
+  private final AtomicBoolean bootstrapInProgress = new AtomicBoolean(false);
+  private final AtomicInteger numBootstraps = new AtomicInteger();
+
   CdcrReplicatorState(final String targetCollection, final String zkHost, final CloudSolrClient targetClient) {
     this.targetCollection = targetCollection;
     this.targetClient = targetClient;
@@ -164,6 +169,24 @@ class CdcrReplicatorState {
     return this.benchmarkTimer;
   }
 
+  /**
+   * @return true if a bootstrap operation is in progress, false otherwise
+   */
+  boolean isBootstrapInProgress() {
+    return bootstrapInProgress.get();
+  }
+
+  void setBootstrapInProgress(boolean inProgress) {
+    if (bootstrapInProgress.compareAndSet(true, false)) {
+      numBootstraps.incrementAndGet();
+    }
+    bootstrapInProgress.set(inProgress);
+  }
+
+  public int getNumBootstraps() {
+    return numBootstraps.get();
+  }
+
   enum ErrorType {
     INTERNAL,
     BAD_REQUEST;

solr/core/src/java/org/apache/solr/handler/CdcrRequestHandler.java

@@ -16,6 +16,7 @@
  */
 package org.apache.solr.handler;
 
+import java.io.Closeable;
 import java.io.IOException;
 import java.lang.invoke.MethodHandles;
 import java.util.ArrayList;
@@ -24,14 +25,20 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.Callable;
+import java.util.concurrent.CancellationException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.locks.Lock;
 
 import org.apache.solr.client.solrj.SolrRequest;
 import org.apache.solr.client.solrj.SolrServerException;
 import org.apache.solr.client.solrj.impl.HttpSolrClient;
+import org.apache.solr.client.solrj.request.AbstractUpdateRequest;
 import org.apache.solr.client.solrj.request.QueryRequest;
+import org.apache.solr.client.solrj.request.UpdateRequest;
 import org.apache.solr.cloud.ZkController;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.cloud.ClusterState;
@@ -41,21 +48,33 @@ import org.apache.solr.common.cloud.ZkNodeProps;
 import org.apache.solr.common.params.CommonParams;
 import org.apache.solr.common.params.ModifiableSolrParams;
 import org.apache.solr.common.params.SolrParams;
+import org.apache.solr.common.params.UpdateParams;
 import org.apache.solr.common.util.ExecutorUtil;
+import org.apache.solr.common.util.IOUtils;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.core.CloseHook;
 import org.apache.solr.core.PluginBag;
 import org.apache.solr.core.SolrCore;
 import org.apache.solr.request.SolrQueryRequest;
 import org.apache.solr.request.SolrRequestHandler;
+import org.apache.solr.request.SolrRequestInfo;
 import org.apache.solr.response.SolrQueryResponse;
 import org.apache.solr.update.CdcrUpdateLog;
 import org.apache.solr.update.UpdateLog;
+import org.apache.solr.update.VersionInfo;
+import org.apache.solr.update.processor.DistributedUpdateProcessor;
 import org.apache.solr.util.DefaultSolrThreadFactory;
 import org.apache.solr.util.plugin.SolrCoreAware;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import static org.apache.solr.handler.admin.CoreAdminHandler.COMPLETED;
+import static org.apache.solr.handler.admin.CoreAdminHandler.FAILED;
+import static org.apache.solr.handler.admin.CoreAdminHandler.RESPONSE;
+import static org.apache.solr.handler.admin.CoreAdminHandler.RESPONSE_MESSAGE;
+import static org.apache.solr.handler.admin.CoreAdminHandler.RESPONSE_STATUS;
+import static org.apache.solr.handler.admin.CoreAdminHandler.RUNNING;
+
 /**
  * <p>
  * This request handler implements the CDCR API and is responsible of the execution of the
@@ -199,6 +218,18 @@ public class CdcrRequestHandler extends RequestHandlerBase implements SolrCoreAw
         this.handleErrorsAction(req, rsp);
         break;
       }
+      case BOOTSTRAP: {
+        this.handleBootstrapAction(req, rsp);
+        break;
+      }
+      case BOOTSTRAP_STATUS:  {
+        this.handleBootstrapStatus(req, rsp);
+        break;
+      }
+      case CANCEL_BOOTSTRAP:  {
+        this.handleCancelBootstrap(req, rsp);
+        break;
+      }
       default: {
         throw new RuntimeException("Unknown action: " + action);
       }
@@ -409,10 +440,20 @@ public class CdcrRequestHandler extends RequestHandlerBase implements SolrCoreAw
     }
 
     UpdateLog ulog = core.getUpdateHandler().getUpdateLog();
+    VersionInfo versionInfo = ulog.getVersionInfo();
     try (UpdateLog.RecentUpdates recentUpdates = ulog.getRecentUpdates()) {
-      List<Long> versions = recentUpdates.getVersions(1);
-      long lastVersion = versions.isEmpty() ? -1 : Math.abs(versions.get(0));
-      rsp.add(CdcrParams.CHECKPOINT, lastVersion);
+      long maxVersionFromRecent = recentUpdates.getMaxRecentVersion();
+      long maxVersionFromIndex = versionInfo.getMaxVersionFromIndex(req.getSearcher());
+      log.info("Found maxVersionFromRecent {} maxVersionFromIndex {}", maxVersionFromRecent, maxVersionFromIndex);
+      // there is no race with ongoing bootstrap because we don't expect any updates to come from the source
+      long maxVersion = Math.max(maxVersionFromIndex, maxVersionFromRecent);
+      if (maxVersion == 0L) {
+        maxVersion = -1;
+      }
+      rsp.add(CdcrParams.CHECKPOINT, maxVersion);
+    } catch (IOException e) {
+      throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, "Action '" + CdcrParams.CdcrAction.SHARDCHECKPOINT +
+          "' could not read max version");
     }
   }
 
@@ -574,6 +615,192 @@ public class CdcrRequestHandler extends RequestHandlerBase implements SolrCoreAw
     rsp.add(CdcrParams.ERRORS, hosts);
   }
 
+  private AtomicBoolean running = new AtomicBoolean();
+  private volatile Future<Boolean> bootstrapFuture;
+  private volatile BootstrapCallable bootstrapCallable;
+
+  private void handleBootstrapAction(SolrQueryRequest req, SolrQueryResponse rsp) throws IOException, SolrServerException {
+    String collectionName = core.getCoreDescriptor().getCloudDescriptor().getCollectionName();
+    String shard = core.getCoreDescriptor().getCloudDescriptor().getShardId();
+    if (!leaderStateManager.amILeader()) {
+      log.warn("Action {} sent to non-leader replica @ {}:{}", CdcrParams.CdcrAction.BOOTSTRAP, collectionName, shard);
+      throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "Action " + CdcrParams.CdcrAction.BOOTSTRAP +
+          " sent to non-leader replica");
+    }
+
+    Runnable runnable = () -> {
+      Lock recoveryLock = req.getCore().getSolrCoreState().getRecoveryLock();
+      boolean locked = recoveryLock.tryLock();
+      try {
+        if (!locked)  {
+          handleCancelBootstrap(req, rsp);
+        } else if (leaderStateManager.amILeader())  {
+          running.set(true);
+          String masterUrl = req.getParams().get(ReplicationHandler.MASTER_URL);
+          bootstrapCallable = new BootstrapCallable(masterUrl, core);
+          bootstrapFuture = core.getCoreDescriptor().getCoreContainer().getUpdateShardHandler().getRecoveryExecutor().submit(bootstrapCallable);
+          try {
+            bootstrapFuture.get();
+          } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            log.warn("Bootstrap was interrupted", e);
+          } catch (ExecutionException e) {
+            log.error("Bootstrap operation failed", e);
+          }
+        } else  {
+          log.error("Action {} sent to non-leader replica @ {}:{}. Aborting bootstrap.", CdcrParams.CdcrAction.BOOTSTRAP, collectionName, shard);
+        }
+      } finally {
+        if (locked) {
+          running.set(false);
+          recoveryLock.unlock();
+        }
+      }
+    };
+
+    try {
+      core.getCoreDescriptor().getCoreContainer().getUpdateShardHandler().getUpdateExecutor().submit(runnable);
+      rsp.add(RESPONSE_STATUS, "submitted");
+    } catch (RejectedExecutionException ree)  {
+      // no problem, we're probably shutting down
+      rsp.add(RESPONSE_STATUS, "failed");
+    }
+  }
+
+  private void handleCancelBootstrap(SolrQueryRequest req, SolrQueryResponse rsp) {
+    BootstrapCallable callable = this.bootstrapCallable;
+    IOUtils.closeQuietly(callable);
+    rsp.add(RESPONSE_STATUS, "cancelled");
+  }
+
+  private void handleBootstrapStatus(SolrQueryRequest req, SolrQueryResponse rsp) throws IOException, SolrServerException {
+    if (running.get()) {
+      rsp.add(RESPONSE_STATUS, RUNNING);
+      return;
+    }
+
+    Future<Boolean> future = bootstrapFuture;
+    BootstrapCallable callable = this.bootstrapCallable;
+    if (future == null) {
+      rsp.add(RESPONSE_STATUS, "notfound");
+      rsp.add(RESPONSE_MESSAGE, "No bootstrap found in running, completed or failed states");
+    } else if (future.isCancelled() || callable.isClosed()) {
+      rsp.add(RESPONSE_STATUS, "cancelled");
+    } else if (future.isDone()) {
+      // could be a normal termination or an exception
+      try {
+        Boolean result = future.get();
+        if (result) {
+          rsp.add(RESPONSE_STATUS, COMPLETED);
+        } else {
+          rsp.add(RESPONSE_STATUS, FAILED);
+        }
+      } catch (InterruptedException e) {
+        // should not happen?
+      } catch (ExecutionException e) {
+        rsp.add(RESPONSE_STATUS, FAILED);
+        rsp.add(RESPONSE, e);
+      } catch (CancellationException ce) {
+        rsp.add(RESPONSE_STATUS, FAILED);
+        rsp.add(RESPONSE_MESSAGE, "Bootstrap was cancelled");
+      }
+    } else {
+      rsp.add(RESPONSE_STATUS, RUNNING);
+    }
+  }
+
+  private static class BootstrapCallable implements Callable<Boolean>, Closeable {
+    private final String masterUrl;
+    private final SolrCore core;
+    private volatile boolean closed = false;
+
+    BootstrapCallable(String masterUrl, SolrCore core) {
+      this.masterUrl = masterUrl;
+      this.core = core;
+    }
+
+    @Override
+    public void close() throws IOException {
+      closed = true;
+      SolrRequestHandler handler = core.getRequestHandler(ReplicationHandler.PATH);
+      ReplicationHandler replicationHandler = (ReplicationHandler) handler;
+      replicationHandler.abortFetch();
+    }
+
+    public boolean isClosed() {
+      return closed;
+    }
+
+    @Override
+    public Boolean call() throws Exception {
+      boolean success = false;
+      UpdateLog ulog = core.getUpdateHandler().getUpdateLog();
+      // we start buffering updates as a safeguard however we do not expect
+      // to receive any updates from the source during bootstrap
+      ulog.bufferUpdates();
+      try {
+        commitOnLeader(masterUrl);
+        // use rep handler directly, so we can do this sync rather than async
+        SolrRequestHandler handler = core.getRequestHandler(ReplicationHandler.PATH);
+        ReplicationHandler replicationHandler = (ReplicationHandler) handler;
+
+        if (replicationHandler == null) {
+          throw new SolrException(SolrException.ErrorCode.SERVICE_UNAVAILABLE,
+              "Skipping recovery, no " + ReplicationHandler.PATH + " handler found");
+        }
+
+        ModifiableSolrParams solrParams = new ModifiableSolrParams();
+        solrParams.set(ReplicationHandler.MASTER_URL, masterUrl);
+        // we do not want the raw tlog files from the source
+        solrParams.set(ReplicationHandler.TLOG_FILES, false);
+
+        success = replicationHandler.doFetch(solrParams, false);
+
+        // this is required because this callable can race with HttpSolrCall#destroy
+        // which clears the request info.
+        // Applying buffered updates fails without the following line because LogReplayer
+        // also tries to set request info and fails with AssertionError
+        SolrRequestInfo.clearRequestInfo();
+
+        Future<UpdateLog.RecoveryInfo> future = ulog.applyBufferedUpdates();
+        if (future == null) {
+          // no replay needed
+          log.info("No replay needed.");
+        } else {
+          log.info("Replaying buffered documents.");
+          // wait for replay
+          UpdateLog.RecoveryInfo report = future.get();
+          if (report.failed) {
+            SolrException.log(log, "Replay failed");
+            throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, "Replay failed");
+          }
+        }
+        return success;
+      } finally {
+        if (closed || !success) {
+          // we cannot apply the buffer in this case because it will introduce newer versions in the
+          // update log and then the source cluster will get those versions via collectioncheckpoint
+          // causing the versions in between to be completely missed
+          boolean dropped = ulog.dropBufferedUpdates();
+          assert dropped;
+        }
+      }
+    }
+
+    private void commitOnLeader(String leaderUrl) throws SolrServerException,
+        IOException {
+      try (HttpSolrClient client = new HttpSolrClient.Builder(leaderUrl).build()) {
+        client.setConnectionTimeout(30000);
+        UpdateRequest ureq = new UpdateRequest();
+        ureq.setParams(new ModifiableSolrParams());
+        ureq.getParams().set(DistributedUpdateProcessor.COMMIT_END_POINT, true);
+        ureq.getParams().set(UpdateParams.OPEN_SEARCHER, false);
+        ureq.setAction(AbstractUpdateRequest.ACTION.COMMIT, false, true).process(
+            client);
+      }
+    }
+  }
+
   @Override
   public String getDescription() {
     return "Manage Cross Data Center Replication";

solr/core/src/java/org/apache/solr/handler/IndexFetcher.java

@@ -82,6 +82,9 @@ import org.apache.solr.core.DirectoryFactory;
 import org.apache.solr.core.DirectoryFactory.DirContext;
 import org.apache.solr.core.IndexDeletionPolicyWrapper;
 import org.apache.solr.core.SolrCore;
+import org.apache.solr.core.snapshots.SolrSnapshotManager;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager.SnapshotMetaData;
 import org.apache.solr.handler.ReplicationHandler.*;
 import org.apache.solr.request.LocalSolrQueryRequest;
 import org.apache.solr.request.SolrQueryRequest;
@@ -468,9 +471,18 @@ public class IndexFetcher {
                 // let the system know we are changing dir's and the old one
                 // may be closed
                 if (indexDir != null) {
-                  LOG.info("removing old index directory " + indexDir);
                   solrCore.getDirectoryFactory().doneWithDirectory(indexDir);
+
+                  SolrSnapshotMetaDataManager snapshotsMgr = solrCore.getSnapshotMetaDataManager();
+                  Collection<SnapshotMetaData> snapshots = snapshotsMgr.listSnapshotsInIndexDir(indexDirPath);
+
+                  // Delete the old index directory only if no snapshot exists in that directory.
+                  if(snapshots.isEmpty()) {
+                    LOG.info("removing old index directory " + indexDir);
                     solrCore.getDirectoryFactory().remove(indexDir);
+                  } else {
+                    SolrSnapshotManager.deleteNonSnapshotIndexFiles(indexDir, snapshots);
+                  }
                 }
               }
 
@@ -738,14 +750,14 @@ public class IndexFetcher {
   }
 
   private void openNewSearcherAndUpdateCommitPoint() throws IOException {
-    SolrQueryRequest req = new LocalSolrQueryRequest(solrCore,
-        new ModifiableSolrParams());
-
     RefCounted<SolrIndexSearcher> searcher = null;
     IndexCommit commitPoint;
+    // must get the latest solrCore object because the one we have might be closed because of a reload
+    // todo stop keeping solrCore around
+    SolrCore core = solrCore.getCoreDescriptor().getCoreContainer().getCore(solrCore.getName());
     try {
       Future[] waitSearcher = new Future[1];
-      searcher = solrCore.getSearcher(true, true, waitSearcher, true);
+      searcher = core.getSearcher(true, true, waitSearcher, true);
       if (waitSearcher[0] != null) {
         try {
           waitSearcher[0].get();
@@ -755,10 +767,10 @@ public class IndexFetcher {
       }
       commitPoint = searcher.get().getIndexReader().getIndexCommit();
     } finally {
-      req.close();
       if (searcher != null) {
         searcher.decref();
       }
+      core.close();
     }
 
     // update the commit point in replication handler

solr/core/src/java/org/apache/solr/handler/MoreLikeThisHandler.java

@@ -125,7 +125,7 @@ public class MoreLikeThisHandler extends RequestHandlerBase
             filters = new ArrayList<>();
             for (String fq : fqs) {
               if (fq != null && fq.trim().length() != 0) {
-                QParser fqp = QParser.getParser(fq, null, req);
+                QParser fqp = QParser.getParser(fq, req);
                 filters.add(fqp.getQuery());
               }
             }

solr/core/src/java/org/apache/solr/handler/ReplicationHandler.java

@@ -87,6 +87,7 @@ import org.apache.solr.core.SolrDeletionPolicy;
 import org.apache.solr.core.SolrEventListener;
 import org.apache.solr.core.backup.repository.BackupRepository;
 import org.apache.solr.core.backup.repository.LocalFileSystemRepository;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager;
 import org.apache.solr.request.SolrQueryRequest;
 import org.apache.solr.response.SolrQueryResponse;
 import org.apache.solr.search.SolrIndexSearcher;
@@ -299,9 +300,7 @@ public class ReplicationHandler extends RequestHandlerBase implements SolrCoreAw
         rsp.add("message","No slave configured");
       }
     } else if (command.equalsIgnoreCase(CMD_ABORT_FETCH)) {
-      IndexFetcher fetcher = currentIndexFetcher;
-      if (fetcher != null){
-        fetcher.abortFetch();
+      if (abortFetch()){
         rsp.add(STATUS, OK_STATUS);
       } else {
         rsp.add(STATUS,ERR_STATUS);
@@ -320,6 +319,16 @@ public class ReplicationHandler extends RequestHandlerBase implements SolrCoreAw
     }
   }
 
+  public boolean abortFetch() {
+    IndexFetcher fetcher = currentIndexFetcher;
+    if (fetcher != null){
+      fetcher.abortFetch();
+      return true;
+    } else {
+      return false;
+    }
+  }
+
   private void deleteSnapshot(ModifiableSolrParams params) {
     String name = params.get(NAME);
     if(name == null) {
@@ -512,12 +521,25 @@ public class ReplicationHandler extends RequestHandlerBase implements SolrCoreAw
         numberToKeep = Integer.MAX_VALUE;
       }
 
+      IndexCommit indexCommit = null;
+      String commitName = params.get(CoreAdminParams.COMMIT_NAME);
+      if (commitName != null) {
+        SolrSnapshotMetaDataManager snapshotMgr = core.getSnapshotMetaDataManager();
+        Optional<IndexCommit> commit = snapshotMgr.getIndexCommitByName(commitName);
+        if(commit.isPresent()) {
+          indexCommit = commit.get();
+        } else {
+          throw new SolrException(ErrorCode.BAD_REQUEST, "Unable to find an index commit with name " + commitName +
+              " for core " + core.getName());
+        }
+      } else {
         IndexDeletionPolicyWrapper delPolicy = core.getDeletionPolicy();
-      IndexCommit indexCommit = delPolicy.getLatestCommit();
+        indexCommit = delPolicy.getLatestCommit();
 
         if (indexCommit == null) {
           indexCommit = req.getSearcher().getIndexReader().getIndexCommit();
         }
+      }
 
       String location = params.get(CoreAdminParams.BACKUP_LOCATION);
       String repoName = params.get(CoreAdminParams.BACKUP_REPOSITORY);
@@ -539,7 +561,7 @@ public class ReplicationHandler extends RequestHandlerBase implements SolrCoreAw
       }
 
       // small race here before the commit point is saved
-      SnapShooter snapShooter = new SnapShooter(repo, core, location, params.get(NAME));
+      SnapShooter snapShooter = new SnapShooter(repo, core, location, params.get(NAME), commitName);
       snapShooter.validateCreateSnapshot();
       snapShooter.createSnapAsync(indexCommit, numberToKeep, (nl) -> snapShootDetails = nl);
 
@@ -644,7 +666,8 @@ public class ReplicationHandler extends RequestHandlerBase implements SolrCoreAw
     rsp.add(CMD_GET_FILE_LIST, result);
 
     // fetch list of tlog files only if cdcr is activated
-    if (core.getUpdateHandler().getUpdateLog() != null && core.getUpdateHandler().getUpdateLog() instanceof CdcrUpdateLog) {
+    if (solrParams.getBool(TLOG_FILES, true) && core.getUpdateHandler().getUpdateLog() != null
+        && core.getUpdateHandler().getUpdateLog() instanceof CdcrUpdateLog) {
       try {
         List<Map<String, Object>> tlogfiles = getTlogFileList(commit);
         LOG.info("Adding tlog files to list: " + tlogfiles);

solr/core/src/java/org/apache/solr/handler/RequestHandlerBase.java

@@ -16,13 +16,17 @@
  */
 package org.apache.solr.handler;
 
+import java.lang.invoke.MethodHandles;
+import java.net.URL;
+import java.util.concurrent.atomic.LongAdder;
+
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.params.SolrParams;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.common.util.SimpleOrderedMap;
 import org.apache.solr.common.util.SuppressForbidden;
-import org.apache.solr.core.PluginInfo;
 import org.apache.solr.core.PluginBag;
+import org.apache.solr.core.PluginInfo;
 import org.apache.solr.core.SolrInfoMBean;
 import org.apache.solr.request.SolrQueryRequest;
 import org.apache.solr.request.SolrRequestHandler;
@@ -35,10 +39,6 @@ import org.apache.solr.util.stats.TimerContext;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.lang.invoke.MethodHandles;
-import java.net.URL;
-import java.util.concurrent.atomic.AtomicLong;
-
 import static org.apache.solr.core.RequestParams.USEPARAM;
 
 /**
@@ -53,10 +53,10 @@ public abstract class RequestHandlerBase implements SolrRequestHandler, SolrInfo
   protected boolean httpCaching = true;
 
   // Statistics
-  private final AtomicLong numRequests = new AtomicLong();
-  private final AtomicLong numServerErrors = new AtomicLong();
-  private final AtomicLong numClientErrors = new AtomicLong();
-  private final AtomicLong numTimeouts = new AtomicLong();
+  private final LongAdder numRequests = new LongAdder();
+  private final LongAdder numServerErrors = new LongAdder();
+  private final LongAdder numClientErrors = new LongAdder();
+  private final LongAdder numTimeouts = new LongAdder();
   private final Timer requestTimes = new Timer();
 
   private final long handlerStart;
@@ -144,7 +144,7 @@ public abstract class RequestHandlerBase implements SolrRequestHandler, SolrInfo
 
   @Override
   public void handleRequest(SolrQueryRequest req, SolrQueryResponse rsp) {
-    numRequests.incrementAndGet();
+    numRequests.increment();
     TimerContext timer = requestTimes.time();
     try {
       if(pluginInfo != null && pluginInfo.attributes.containsKey(USEPARAM)) req.getContext().put(USEPARAM,pluginInfo.attributes.get(USEPARAM));
@@ -158,7 +158,7 @@ public abstract class RequestHandlerBase implements SolrRequestHandler, SolrInfo
         Object partialResults = header.get(SolrQueryResponse.RESPONSE_HEADER_PARTIAL_RESULTS_KEY);
         boolean timedOut = partialResults == null ? false : (Boolean)partialResults;
         if( timedOut ) {
-          numTimeouts.incrementAndGet();
+          numTimeouts.increment();
           rsp.setHttpCaching(false);
         }
       }
@@ -185,9 +185,9 @@ public abstract class RequestHandlerBase implements SolrRequestHandler, SolrInfo
         SolrException.log(log, e);
 
         if (isServerError) {
-          numServerErrors.incrementAndGet();
+          numServerErrors.increment();
         } else {
-          numClientErrors.incrementAndGet();
+          numClientErrors.increment();
         }
       }
     }

solr/core/src/java/org/apache/solr/handler/RestoreCore.java

@@ -19,6 +19,7 @@ package org.apache.solr.handler;
 import java.lang.invoke.MethodHandles;
 import java.net.URI;
 import java.text.SimpleDateFormat;
+import java.util.Collection;
 import java.util.Date;
 import java.util.Locale;
 import java.util.concurrent.Callable;
@@ -32,6 +33,9 @@ import org.apache.solr.common.SolrException;
 import org.apache.solr.core.DirectoryFactory;
 import org.apache.solr.core.SolrCore;
 import org.apache.solr.core.backup.repository.BackupRepository;
+import org.apache.solr.core.snapshots.SolrSnapshotManager;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager.SnapshotMetaData;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -63,6 +67,7 @@ public class RestoreCore implements Callable<Boolean> {
     String restoreIndexName = "restore." + dateFormat.format(new Date());
     String restoreIndexPath = core.getDataDir() + restoreIndexName;
 
+    String indexDirPath = core.getIndexDir();
     Directory restoreIndexDir = null;
     Directory indexDir = null;
     try {
@@ -71,7 +76,7 @@ public class RestoreCore implements Callable<Boolean> {
           DirectoryFactory.DirContext.DEFAULT, core.getSolrConfig().indexConfig.lockType);
 
       //Prefer local copy.
-      indexDir = core.getDirectoryFactory().get(core.getIndexDir(),
+      indexDir = core.getDirectoryFactory().get(indexDirPath,
           DirectoryFactory.DirContext.DEFAULT, core.getSolrConfig().indexConfig.lockType);
 
       //Move all files from backupDir to restoreIndexDir
@@ -130,7 +135,16 @@ public class RestoreCore implements Callable<Boolean> {
       }
       if (success) {
         core.getDirectoryFactory().doneWithDirectory(indexDir);
+
+        SolrSnapshotMetaDataManager snapshotsMgr = core.getSnapshotMetaDataManager();
+        Collection<SnapshotMetaData> snapshots = snapshotsMgr.listSnapshotsInIndexDir(indexDirPath);
+
+        // Delete the old index directory only if no snapshot exists in that directory.
+        if (snapshots.isEmpty()) {
           core.getDirectoryFactory().remove(indexDir);
+        } else {
+          SolrSnapshotManager.deleteNonSnapshotIndexFiles(indexDir, snapshots);
+        }
       }
 
       return true;

solr/core/src/java/org/apache/solr/handler/SchemaHandler.java

@@ -185,7 +185,7 @@ public class SchemaHandler extends RequestHandlerBase implements SolrCoreAware,
           if (parts.get(0).isEmpty()) parts.remove(0);
           if (parts.size() > 1 && level2.containsKey(parts.get(1))) {
             String realName = parts.get(1);
-            String fieldName = IndexSchema.SchemaProps.nameMapping.get(realName);
+            String fieldName = IndexSchema.nameMapping.get(realName);
 
             String pathParam = level2.get(realName);
             if (parts.size() > 2) {

solr/core/src/java/org/apache/solr/handler/SnapShooter.java

@@ -26,12 +26,14 @@ import java.util.Collections;
 import java.util.Date;
 import java.util.List;
 import java.util.Locale;
+import java.util.Optional;
 import java.util.function.Consumer;
 
 import com.google.common.base.Preconditions;
 import org.apache.lucene.index.IndexCommit;
 import org.apache.lucene.store.Directory;
 import org.apache.solr.common.SolrException;
+import org.apache.solr.common.SolrException.ErrorCode;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.core.DirectoryFactory.DirContext;
 import org.apache.solr.core.IndexDeletionPolicyWrapper;
@@ -39,6 +41,7 @@ import org.apache.solr.core.SolrCore;
 import org.apache.solr.core.backup.repository.BackupRepository;
 import org.apache.solr.core.backup.repository.BackupRepository.PathType;
 import org.apache.solr.core.backup.repository.LocalFileSystemRepository;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager;
 import org.apache.solr.search.SolrIndexSearcher;
 import org.apache.solr.util.RefCounted;
 import org.slf4j.Logger;
@@ -59,6 +62,7 @@ public class SnapShooter {
   private URI baseSnapDirPath = null;
   private URI snapshotDirPath = null;
   private BackupRepository backupRepo = null;
+  private String commitName; // can be null
 
   @Deprecated
   public SnapShooter(SolrCore core, String location, String snapshotName) {
@@ -71,14 +75,14 @@ public class SnapShooter {
     } else {
       snapDirStr = core.getCoreDescriptor().getInstanceDir().resolve(location).normalize().toString();
     }
-    initialize(new LocalFileSystemRepository(), core, snapDirStr, snapshotName);
+    initialize(new LocalFileSystemRepository(), core, snapDirStr, snapshotName, null);
   }
 
-  public SnapShooter(BackupRepository backupRepo, SolrCore core, String location, String snapshotName) {
-    initialize(backupRepo, core, location, snapshotName);
+  public SnapShooter(BackupRepository backupRepo, SolrCore core, String location, String snapshotName, String commitName) {
+    initialize(backupRepo, core, location, snapshotName, commitName);
   }
 
-  private void initialize(BackupRepository backupRepo, SolrCore core, String location, String snapshotName) {
+  private void initialize(BackupRepository backupRepo, SolrCore core, String location, String snapshotName, String commitName) {
     this.solrCore = Preconditions.checkNotNull(core);
     this.backupRepo = Preconditions.checkNotNull(backupRepo);
     this.baseSnapDirPath = backupRepo.createURI(Preconditions.checkNotNull(location)).normalize();
@@ -90,6 +94,7 @@ public class SnapShooter {
       directoryName = "snapshot." + fmt.format(new Date());
     }
     this.snapshotDirPath = backupRepo.createURI(location, directoryName);
+    this.commitName = commitName;
   }
 
   public BackupRepository getBackupRepository() {
@@ -145,10 +150,19 @@ public class SnapShooter {
   }
 
   public NamedList createSnapshot() throws Exception {
-    IndexDeletionPolicyWrapper deletionPolicy = solrCore.getDeletionPolicy();
     RefCounted<SolrIndexSearcher> searcher = solrCore.getSearcher();
     try {
+      if (commitName != null) {
+        SolrSnapshotMetaDataManager snapshotMgr = solrCore.getSnapshotMetaDataManager();
+        Optional<IndexCommit> commit = snapshotMgr.getIndexCommitByName(commitName);
+        if(commit.isPresent()) {
+          return createSnapshot(commit.get());
+        }
+        throw new SolrException(ErrorCode.SERVER_ERROR, "Unable to find an index commit with name " + commitName +
+            " for core " + solrCore.getName());
+      } else {
         //TODO should we try solrCore.getDeletionPolicy().getLatestCommit() first?
+        IndexDeletionPolicyWrapper deletionPolicy = solrCore.getDeletionPolicy();
         IndexCommit indexCommit = searcher.get().getIndexReader().getIndexCommit();
         deletionPolicy.saveCommitPoint(indexCommit.getGeneration());
         try {
@@ -156,6 +170,7 @@ public class SnapShooter {
         } finally {
           deletionPolicy.releaseCommitPoint(indexCommit.getGeneration());
         }
+      }
     } finally {
       searcher.decref();
     }

solr/core/src/java/org/apache/solr/handler/StreamHandler.java

@@ -122,6 +122,8 @@ public class StreamHandler extends RequestHandlerBase implements SolrCoreAware,
       .withFunctionName("intersect", IntersectStream.class)
       .withFunctionName("complement", ComplementStream.class)
       .withFunctionName("sort", SortStream.class)
+      .withFunctionName("train", TextLogitStream.class)
+      .withFunctionName("features", FeaturesSelectionStream.class)
       .withFunctionName("daemon", DaemonStream.class)
       .withFunctionName("shortestPath", ShortestPathStream.class)
       .withFunctionName("gatherNodes", GatherNodesStream.class)

solr/core/src/java/org/apache/solr/handler/admin/CollectionsHandler.java

@@ -714,10 +714,8 @@ public class CollectionsHandler extends RequestHandlerBase implements Permission
       String location = repository.getBackupLocation(req.getParams().get(CoreAdminParams.BACKUP_LOCATION));
       if (location == null) {
         //Refresh the cluster property file to make sure the value set for location is the latest
-        h.coreContainer.getZkController().getZkStateReader().forceUpdateClusterProperties();
-
         // Check if the location is specified in the cluster property.
-        location = h.coreContainer.getZkController().getZkStateReader().getClusterProperty(CoreAdminParams.BACKUP_LOCATION, null);
+        location = new ClusterProperties(h.coreContainer.getZkController().getZkClient()).getClusterProperty(CoreAdminParams.BACKUP_LOCATION, null);
         if (location == null) {
           throw new SolrException(ErrorCode.BAD_REQUEST, "'location' is not specified as a query"
               + " parameter or as a default repository property or as a cluster property.");
@@ -755,10 +753,8 @@ public class CollectionsHandler extends RequestHandlerBase implements Permission
       String location = repository.getBackupLocation(req.getParams().get(CoreAdminParams.BACKUP_LOCATION));
       if (location == null) {
         //Refresh the cluster property file to make sure the value set for location is the latest
-        h.coreContainer.getZkController().getZkStateReader().forceUpdateClusterProperties();
-
         // Check if the location is specified in the cluster property.
-        location = h.coreContainer.getZkController().getZkStateReader().getClusterProperty("location", null);
+        location = new ClusterProperties(h.coreContainer.getZkController().getZkClient()).getClusterProperty("location", null);
         if (location == null) {
           throw new SolrException(ErrorCode.BAD_REQUEST, "'location' is not specified as a query"
               + " parameter or as a default repository property or as a cluster property.");

solr/core/src/java/org/apache/solr/handler/admin/CoreAdminOperation.java

@@ -34,6 +34,7 @@ import java.util.concurrent.Future;
 import com.google.common.collect.Lists;
 import org.apache.commons.lang.StringUtils;
 import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexCommit;
 import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.IOUtils;
@@ -59,9 +60,13 @@ import org.apache.solr.core.CachingDirectoryFactory;
 import org.apache.solr.core.CoreContainer;
 import org.apache.solr.core.CoreDescriptor;
 import org.apache.solr.core.DirectoryFactory;
+import org.apache.solr.core.DirectoryFactory.DirContext;
 import org.apache.solr.core.SolrCore;
 import org.apache.solr.core.SolrResourceLoader;
 import org.apache.solr.core.backup.repository.BackupRepository;
+import org.apache.solr.core.snapshots.SolrSnapshotManager;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager;
+import org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager.SnapshotMetaData;
 import org.apache.solr.handler.RestoreCore;
 import org.apache.solr.handler.SnapShooter;
 import org.apache.solr.handler.admin.CoreAdminHandler.CoreAdminOp;
@@ -794,20 +799,24 @@ enum CoreAdminOperation implements CoreAdminOp {
           + " parameter or as a default repository property");
     }
 
+      // An optional parameter to describe the snapshot to be backed-up. If this
+      // parameter is not supplied, the latest index commit is backed-up.
+      String commitName = params.get(CoreAdminParams.COMMIT_NAME);
+
       try (SolrCore core = it.handler.coreContainer.getCore(cname)) {
-      SnapShooter snapShooter = new SnapShooter(repository, core, location, name);
+        SnapShooter snapShooter = new SnapShooter(repository, core, location, name, commitName);
         // validateCreateSnapshot will create parent dirs instead of throw; that choice is dubious.
         //  But we want to throw. One reason is that
         //  this dir really should, in fact must, already exist here if triggered via a collection backup on a shared
         //  file system. Otherwise, perhaps the FS location isn't shared -- we want an error.
         if (!snapShooter.getBackupRepository().exists(snapShooter.getLocation())) {
-        throw new SolrException(ErrorCode.BAD_REQUEST,
+          throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
               "Directory to contain snapshots doesn't exist: " + snapShooter.getLocation());
         }
         snapShooter.validateCreateSnapshot();
         snapShooter.createSnapshot();
       } catch (Exception e) {
-      throw new SolrException(ErrorCode.SERVER_ERROR,
+        throw new SolrException(SolrException.ErrorCode.SERVER_ERROR,
             "Failed to backup core=" + cname + " because " + e, e);
       }
   }),
@@ -845,6 +854,92 @@ enum CoreAdminOperation implements CoreAdminOp {
         throw new SolrException(ErrorCode.SERVER_ERROR, "Failed to restore core=" + core.getName());
       }
     }
+  }),
+  CREATESNAPSHOT_OP(CREATESNAPSHOT, it -> {
+    CoreContainer cc = it.handler.getCoreContainer();
+    final SolrParams params = it.req.getParams();
+
+    String commitName = params.required().get(CoreAdminParams.COMMIT_NAME);
+    String cname = params.required().get(CoreAdminParams.CORE);
+    try (SolrCore core = cc.getCore(cname)) {
+      if (core == null) {
+        throw new SolrException(ErrorCode.BAD_REQUEST, "Unable to locate core " + cname);
+      }
+
+      String indexDirPath = core.getIndexDir();
+      IndexCommit ic = core.getDeletionPolicy().getLatestCommit();
+      if (ic == null) {
+        RefCounted<SolrIndexSearcher> searcher = core.getSearcher();
+        try {
+          ic = searcher.get().getIndexReader().getIndexCommit();
+        } finally {
+          searcher.decref();
+        }
+      }
+      SolrSnapshotMetaDataManager mgr = core.getSnapshotMetaDataManager();
+      mgr.snapshot(commitName, indexDirPath, ic.getGeneration());
+
+      it.rsp.add("core", core.getName());
+      it.rsp.add("commitName", commitName);
+      it.rsp.add("indexDirPath", indexDirPath);
+      it.rsp.add("generation", ic.getGeneration());
+    }
+  }),
+  DELETESNAPSHOT_OP(DELETESNAPSHOT, it -> {
+    CoreContainer cc = it.handler.getCoreContainer();
+    final SolrParams params = it.req.getParams();
+
+    String commitName = params.required().get(CoreAdminParams.COMMIT_NAME);
+    String cname = params.required().get(CoreAdminParams.CORE);
+    try (SolrCore core = cc.getCore(cname)) {
+      if (core == null) {
+        throw new SolrException(ErrorCode.BAD_REQUEST, "Unable to locate core " + cname);
+      }
+
+      SolrSnapshotMetaDataManager mgr = core.getSnapshotMetaDataManager();
+      Optional<SnapshotMetaData> metadata = mgr.release(commitName);
+      if (metadata.isPresent()) {
+        long gen = metadata.get().getGenerationNumber();
+        String indexDirPath = metadata.get().getIndexDirPath();
+
+        // If the directory storing the snapshot is not the same as the *current* core
+        // index directory, then delete the files corresponding to this snapshot.
+        // Otherwise we leave the index files related to snapshot as is (assuming the
+        // underlying Solr IndexDeletionPolicy will clean them up appropriately).
+        if (!indexDirPath.equals(core.getIndexDir())) {
+          Directory d = core.getDirectoryFactory().get(indexDirPath, DirContext.DEFAULT, DirectoryFactory.LOCK_TYPE_NONE);
+          try {
+            SolrSnapshotManager.deleteIndexFiles(d, mgr.listSnapshotsInIndexDir(indexDirPath), gen);
+          } finally {
+            core.getDirectoryFactory().release(d);
+          }
+        }
+      }
+    }
+  }),
+  LISTSNAPSHOTS_OP(LISTSNAPSHOTS, it -> {
+    CoreContainer cc = it.handler.getCoreContainer();
+    final SolrParams params = it.req.getParams();
+
+    String cname = params.required().get(CoreAdminParams.CORE);
+    try ( SolrCore core = cc.getCore(cname) ) {
+      if (core == null) {
+        throw new SolrException(ErrorCode.BAD_REQUEST, "Unable to locate core " + cname);
+      }
+
+      SolrSnapshotMetaDataManager mgr = core.getSnapshotMetaDataManager();
+      NamedList result = new NamedList();
+      for (String name : mgr.listSnapshots()) {
+        Optional<SnapshotMetaData> metadata = mgr.getSnapshotMetaData(name);
+        if ( metadata.isPresent() ) {
+          NamedList<String> props = new NamedList<>();
+          props.add("generation", String.valueOf(metadata.get().getGenerationNumber()));
+          props.add("indexDirPath", metadata.get().getIndexDirPath());
+          result.add(name, props);
+        }
+      }
+      it.rsp.add("snapshots", result);
+    }
   });
 
   final CoreAdminParams.CoreAdminAction action;

solr/core/src/java/org/apache/solr/handler/component/ExpandComponent.java

@@ -176,7 +176,7 @@ public class ExpandComponent extends SearchComponent implements PluginInfoInitia
       query = rb.getQuery();
     } else {
       try {
-        QParser parser = QParser.getParser(qs, null, req);
+        QParser parser = QParser.getParser(qs, req);
         query = parser.getQuery();
       } catch (Exception e) {
         throw new IOException(e);
@@ -198,7 +198,7 @@ public class ExpandComponent extends SearchComponent implements PluginInfoInitia
       try {
         for (String fq : fqs) {
           if (fq != null && fq.trim().length() != 0 && !fq.equals("*:*")) {
-            QParser fqp = QParser.getParser(fq, null, req);
+            QParser fqp = QParser.getParser(fq, req);
             newFilters.add(fqp.getQuery());
           }
         }

solr/core/src/java/org/apache/solr/handler/component/QueryComponent.java

@@ -202,7 +202,7 @@ public class QueryComponent extends SearchComponent
         filters = filters == null ? new ArrayList<Query>(fqs.length) : new ArrayList<>(filters);
         for (String fq : fqs) {
           if (fq != null && fq.trim().length()!=0) {
-            QParser fqp = QParser.getParser(fq, null, req);
+            QParser fqp = QParser.getParser(fq, req);
             filters.add(fqp.getQuery());
           }
         }

solr/core/src/java/org/apache/solr/handler/component/RealTimeGetComponent.java

@@ -158,7 +158,7 @@ public class RealTimeGetComponent extends SearchComponent
         filters = filters == null ? new ArrayList<Query>(fqs.length) : new ArrayList<>(filters);
         for (String fq : fqs) {
           if (fq != null && fq.trim().length()!=0) {
-            QParser fqp = QParser.getParser(fq, null, req);
+            QParser fqp = QParser.getParser(fq, req);
             filters.add(fqp.getQuery());
           }
         }
@@ -249,7 +249,8 @@ public class RealTimeGetComponent extends SearchComponent
          docid = segid + ctx.docBase;
 
          if (rb.getFilters() != null) {
-           for (Query q : rb.getFilters()) {
+           for (Query raw : rb.getFilters()) {
+             Query q = raw.rewrite(searcher.getIndexReader());
              Scorer scorer = searcher.createWeight(q, false, 1f).scorer(ctx);
              if (scorer == null || segid != scorer.iterator().advance(segid)) {
                // filter doesn't match.
@@ -448,7 +449,7 @@ public class RealTimeGetComponent extends SearchComponent
     ZkController zkController = rb.req.getCore().getCoreDescriptor().getCoreContainer().getZkController();
 
     // if shards=... then use that
-    if (zkController != null && params.get("shards") == null) {
+    if (zkController != null && params.get(ShardParams.SHARDS) == null) {
       CloudDescriptor cloudDescriptor = rb.req.getCore().getCoreDescriptor().getCloudDescriptor();
 
       String collection = cloudDescriptor.getCollectionName();
@@ -470,32 +471,18 @@ public class RealTimeGetComponent extends SearchComponent
 
       for (Map.Entry<String,List<String>> entry : sliceToId.entrySet()) {
         String shard = entry.getKey();
-        String shardIdList = StrUtils.join(entry.getValue(), ',');
 
-        ShardRequest sreq = new ShardRequest();
-
-        sreq.purpose = 1;
+        ShardRequest sreq = createShardRequest(rb, entry.getValue());
         // sreq.shards = new String[]{shard};    // TODO: would be nice if this would work...
         sreq.shards = sliceToShards(rb, collection, shard);
         sreq.actualShards = sreq.shards;
-        sreq.params = new ModifiableSolrParams();
-        sreq.params.set(ShardParams.SHARDS_QT,"/get");      // TODO: how to avoid hardcoding this and hit the same handler?
-        sreq.params.set("distrib",false);
-        sreq.params.set("ids", shardIdList);
         
         rb.addRequest(this, sreq);
       }      
     } else {
-      String shardIdList = StrUtils.join(reqIds.allIds, ',');
-      ShardRequest sreq = new ShardRequest();
-
-      sreq.purpose = 1;
+      ShardRequest sreq = createShardRequest(rb, reqIds.allIds);
       sreq.shards = null;  // ALL
       sreq.actualShards = sreq.shards;
-      sreq.params = new ModifiableSolrParams();
-      sreq.params.set(ShardParams.SHARDS_QT,"/get");      // TODO: how to avoid hardcoding this and hit the same handler?
-      sreq.params.set("distrib",false);
-      sreq.params.set("ids", shardIdList);
 
       rb.addRequest(this, sreq);
     }
@@ -503,6 +490,28 @@ public class RealTimeGetComponent extends SearchComponent
     return ResponseBuilder.STAGE_DONE;
   }
 
+  /**
+   * Helper method for creating a new ShardRequest for the specified ids, based on the params 
+   * specified for the current request.  The new ShardRequest does not yet know anything about 
+   * which shard/slice it will be sent to.
+   */
+  private ShardRequest createShardRequest(final ResponseBuilder rb, final List<String> ids) {
+    final ShardRequest sreq = new ShardRequest();
+    sreq.purpose = 1;
+    sreq.params = new ModifiableSolrParams(rb.req.getParams());
+
+    // TODO: how to avoid hardcoding this and hit the same handler?
+    sreq.params.set(ShardParams.SHARDS_QT,"/get");      
+    sreq.params.set("distrib",false);
+
+    sreq.params.remove(ShardParams.SHARDS);
+    sreq.params.remove("id");
+    sreq.params.remove("ids");
+    sreq.params.set("ids", StrUtils.join(ids, ','));
+    
+    return sreq;
+  }
+  
   private String[] sliceToShards(ResponseBuilder rb, String collection, String slice) {
     String lookup = collection + '_' + slice;  // seems either form may be filled in rb.slices?
     

solr/core/src/java/org/apache/solr/handler/component/SpellCheckComponent.java

@@ -60,7 +60,6 @@ import org.apache.solr.schema.FieldType;
 import org.apache.solr.schema.IndexSchema;
 import org.apache.solr.search.DocSet;
 import org.apache.solr.search.QParser;
-import org.apache.solr.search.QParserPlugin;
 import org.apache.solr.search.SyntaxError;
 import org.apache.solr.search.SolrIndexSearcher;
 import org.apache.solr.spelling.AbstractLuceneSpellChecker;
@@ -242,7 +241,7 @@ public class SpellCheckComponent extends SearchComponent implements SolrCoreAwar
         try {
           if (maxResultsFilterQueryString != null) {
             // Get the default Lucene query parser
-            QParser parser = QParser.getParser(maxResultsFilterQueryString, QParserPlugin.DEFAULT_QTYPE, rb.req);              
+            QParser parser = QParser.getParser(maxResultsFilterQueryString, rb.req);
             DocSet s = searcher.getDocSet(parser.getQuery());
             maxResultsByFilters = s.size();
           } else {

solr/core/src/java/org/apache/solr/request/SimpleFacets.java

@@ -321,7 +321,7 @@ public class SimpleFacets {
   public void getFacetQueryCount(ParsedParams parsed, NamedList<Integer> res) throws SyntaxError, IOException {
     // TODO: slight optimization would prevent double-parsing of any localParams
     // TODO: SOLR-7753
-    Query qobj = QParser.getParser(parsed.facetValue, null, req).getQuery();
+    Query qobj = QParser.getParser(parsed.facetValue, req).getQuery();
 
     if (qobj == null) {
       res.add(parsed.key, 0);

solr/core/src/java/org/apache/solr/response/transform/ChildDocTransformerFactory.java

@@ -77,7 +77,7 @@ public class ChildDocTransformerFactory extends TransformerFactory {
 
     BitSetProducer parentsFilter = null;
     try {
-      Query parentFilterQuery = QParser.getParser( parentFilter, null, req).getQuery();
+      Query parentFilterQuery = QParser.getParser( parentFilter, req).getQuery();
       parentsFilter = new QueryBitSetProducer(new QueryWrapperFilter(parentFilterQuery));
     } catch (SyntaxError syntaxError) {
       throw new SolrException( ErrorCode.BAD_REQUEST, "Failed to create correct parent filter query" );
@@ -86,7 +86,7 @@ public class ChildDocTransformerFactory extends TransformerFactory {
     Query childFilterQuery = null;
     if(childFilter != null) {
       try {
-        childFilterQuery = QParser.getParser( childFilter, null, req).getQuery();
+        childFilterQuery = QParser.getParser( childFilter, req).getQuery();
       } catch (SyntaxError syntaxError) {
         throw new SolrException( ErrorCode.BAD_REQUEST, "Failed to create correct child filter query" );
       }

solr/core/src/java/org/apache/solr/response/transform/SubQueryAugmenterFactory.java

@@ -76,6 +76,15 @@ import org.apache.solr.search.TermsQParserPlugin;
  * its' native parameters like <code>collection, shards</code> for subquery, eg<br>
  *  <code>q=*:*&amp;fl=*,foo:[subquery]&amp;foo.q=cloud&amp;foo.collection=departments</code>
  *
+ * <h3>When used in Real Time Get</h3>
+ * <p>
+ * When used in the context of a Real Time Get, the <i>values</i> from each document that are used 
+ * in the qubquery are the "real time" values (possibly from the transaction log), but the query 
+ * itself is still executed against the currently open searcher.  Note that this means if a 
+ * document is updated but not yet committed, an RTG request for that document that uses 
+ * <code>[subquery]</code> could include the older (committed) version of that document, 
+ * with differnet field values, in the subquery results.
+ * </p>
  */
 public class SubQueryAugmenterFactory extends TransformerFactory{
 
@@ -304,6 +313,14 @@ class SubQueryAugmenter extends DocTransformer {
     return name;
   }
   
+  /**
+   * Returns false -- this transformer does use an IndexSearcher, but it does not (neccessarily) need 
+   * the searcher from the ResultContext of the document being returned.  Instead we use the current 
+   * "live" searcher for the specified core.
+   */
+  @Override
+  public boolean needsSolrIndexSearcher() { return false; }
+
   @Override
   public void transform(SolrDocument doc, int docid, float score) {
 

solr/core/src/java/org/apache/solr/schema/IndexSchema.java

@@ -1500,10 +1500,12 @@ public class IndexSchema {
               (v1, v2) -> v2,
               LinkedHashMap::new));
     }
-    public static Map<String,String> nameMapping = Collections.unmodifiableMap(Stream.of(Handler.values())
-        .collect(Collectors.toMap(Handler::getNameLower , Handler::getRealName)));
   }
 
+  public static Map<String,String> nameMapping = Collections.unmodifiableMap(Stream.of(SchemaProps.Handler.values())
+      .collect(Collectors.toMap(SchemaProps.Handler::getNameLower , SchemaProps.Handler::getRealName)));
+
+
   public Map<String, Object> getNamedPropertyValues(String name, SolrParams params) {
     return new SchemaProps(name, params, this).toMap();