LUCENE-10032: Remove leafDocMaps from MergeState (#222)

These maps are no longer useful after LUCENE-8505.

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

@@ -4138,7 +4138,6 @@ public class IndexWriter
       assert rld != null : "seg=" + info.info.name;
 
       MergeState.DocMap segDocMap = mergeState.docMaps[i];
-      MergeState.DocMap segLeafDocMap = mergeState.leafDocMaps[i];
 
       carryOverHardDeletes(
           mergedDeletesAndUpdates,
@@ -4146,8 +4145,7 @@ public class IndexWriter
           mergeState.liveDocs[i],
           merge.getMergeReader().get(i).hardLiveDocs,
           rld.getHardLiveDocs(),
-          segDocMap,
-          segLeafDocMap);
+          segDocMap);
 
       // Now carry over all doc values updates that were resolved while we were merging, remapping
       // the docIDs to the newly merged docIDs.
@@ -4200,7 +4198,7 @@ public class IndexWriter
           DocValuesFieldUpdates.Iterator it = updates.iterator();
           int doc;
           while ((doc = it.nextDoc()) != NO_MORE_DOCS) {
-            int mappedDoc = segDocMap.get(segLeafDocMap.get(doc));
+            int mappedDoc = segDocMap.get(doc);
             if (mappedDoc != -1) {
               if (it.hasValue()) {
                 // not deleted
@@ -4250,8 +4248,7 @@ public class IndexWriter
       Bits mergeLiveDocs, // the liveDocs used to build the segDocMaps
       Bits prevHardLiveDocs, // the hard deletes when the merge reader was pulled
       Bits currentHardLiveDocs, // the current hard deletes
-      MergeState.DocMap segDocMap,
-      MergeState.DocMap segLeafDocMap)
+      MergeState.DocMap segDocMap)
       throws IOException {
 
     assert mergeLiveDocs == null || mergeLiveDocs.length() == maxDoc;
@@ -4293,7 +4290,7 @@ public class IndexWriter
             assert currentHardLiveDocs.get(j) == false;
           } else if (carryOverDelete.test(j)) {
             // the document was deleted while we were merging:
-            mergedReadersAndUpdates.delete(segDocMap.get(segLeafDocMap.get(j)));
+            mergedReadersAndUpdates.delete(segDocMap.get(j));
           }
         }
       }
@@ -4303,7 +4300,7 @@ public class IndexWriter
       // does:
       for (int j = 0; j < maxDoc; j++) {
         if (carryOverDelete.test(j)) {
-          mergedReadersAndUpdates.delete(segDocMap.get(segLeafDocMap.get(j)));
+          mergedReadersAndUpdates.delete(segDocMap.get(j));
         }
       }
     }

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

@@ -19,7 +19,6 @@ package org.apache.lucene.index;
 import static org.apache.lucene.index.IndexWriter.isCongruentSort;
 
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
 import org.apache.lucene.codecs.DocValuesProducer;
@@ -45,10 +44,6 @@ public class MergeState {
   /** Maps document IDs from old segments to document IDs in the new segment */
   public final DocMap[] docMaps;
 
-  // Only used by IW when it must remap deletes that arrived against the merging segments while a
-  // merge was running:
-  final DocMap[] leafDocMaps;
-
   /** {@link SegmentInfo} of the newly merged segment. */
   public final SegmentInfo segmentInfo;
 
@@ -92,15 +87,11 @@ public class MergeState {
   public boolean needsIndexSort;
 
   /** Sole constructor. */
-  MergeState(List<CodecReader> originalReaders, SegmentInfo segmentInfo, InfoStream infoStream)
+  MergeState(List<CodecReader> readers, SegmentInfo segmentInfo, InfoStream infoStream)
       throws IOException {
-
+    verifyIndexSort(readers, segmentInfo);
     this.infoStream = infoStream;
-
-    final Sort indexSort = segmentInfo.getIndexSort();
-    int numReaders = originalReaders.size();
-    leafDocMaps = new DocMap[numReaders];
-    List<CodecReader> readers = maybeSortReaders(originalReaders, segmentInfo);
+    int numReaders = readers.size();
 
     maxDocs = new int[numReaders];
     fieldsProducers = new FieldsProducer[numReaders];
@@ -158,7 +149,7 @@ public class MergeState {
     segmentInfo.setMaxDoc(numDocs);
 
     this.segmentInfo = segmentInfo;
-    this.docMaps = buildDocMaps(readers, indexSort);
+    this.docMaps = buildDocMaps(readers, segmentInfo.getIndexSort());
   }
 
   // Remap docIDs around deletions
@@ -226,28 +217,12 @@ public class MergeState {
     }
   }
 
-  private List<CodecReader> maybeSortReaders(
-      List<CodecReader> originalReaders, SegmentInfo segmentInfo) throws IOException {
-
-    // Default to identity:
-    for (int i = 0; i < originalReaders.size(); i++) {
-      leafDocMaps[i] =
-          new DocMap() {
-            @Override
-            public int get(int docID) {
-              return docID;
-            }
-          };
-    }
-
+  private static void verifyIndexSort(List<CodecReader> readers, SegmentInfo segmentInfo) {
     Sort indexSort = segmentInfo.getIndexSort();
     if (indexSort == null) {
-      return originalReaders;
+      return;
     }
-
-    List<CodecReader> readers = new ArrayList<>(originalReaders.size());
-
-    for (CodecReader leaf : originalReaders) {
+    for (CodecReader leaf : readers) {
       Sort segmentSort = leaf.getMetaData().getSort();
       if (segmentSort == null || isCongruentSort(indexSort, segmentSort) == false) {
         throw new IllegalArgumentException(
@@ -256,10 +231,7 @@ public class MergeState {
                 + " but to-be-merged segment has sort="
                 + (segmentSort == null ? "null" : segmentSort));
       }
-      readers.add(leaf);
     }
-
-    return readers;
   }
 
   /** A map of doc IDs. */