[Backport 2.x] Bug fix for total hits counts mismatch in hybrid query

CHANGELOG.md

@@ -19,6 +19,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Optimize parameter parsing in text chunking processor ([#733](https://github.com/opensearch-project/neural-search/pull/733))
 - Use lazy initialization for priority queue of hits and scores to improve latencies by 20% ([#746](https://github.com/opensearch-project/neural-search/pull/746))
 ### Bug Fixes
+- Total hit count fix in Hybrid Query ([756](https://github.com/opensearch-project/neural-search/pull/756))
 ### Infrastructure
 ### Documentation
 ### Maintenance

src/main/java/org/opensearch/neuralsearch/processor/combination/ScoreCombiner.java

@@ -5,12 +5,10 @@
 package org.opensearch.neuralsearch.processor.combination;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
 import java.util.stream.Collectors;
 
 import org.apache.lucene.search.ScoreDoc;
@@ -80,16 +78,15 @@ private List<ScoreDoc> getCombinedScoreDocs(
         final CompoundTopDocs compoundQueryTopDocs,
         final Map<Integer, Float> combinedNormalizedScoresByDocId,
         final List<Integer> sortedScores,
-        final int maxHits
+        final long maxHits
     ) {
-        ScoreDoc[] finalScoreDocs = new ScoreDoc[maxHits];
-
+        List<ScoreDoc> scoreDocs = new ArrayList<>();
         int shardId = compoundQueryTopDocs.getScoreDocs().get(0).shardIndex;
         for (int j = 0; j < maxHits && j < sortedScores.size(); j++) {
             int docId = sortedScores.get(j);
-            finalScoreDocs[j] = new ScoreDoc(docId, combinedNormalizedScoresByDocId.get(docId), shardId);
+            scoreDocs.add(new ScoreDoc(docId, combinedNormalizedScoresByDocId.get(docId), shardId));
         }
-        return Arrays.stream(finalScoreDocs).collect(Collectors.toList());
+        return scoreDocs;
     }
 
     public Map<Integer, float[]> getNormalizedScoresPerDocument(final List<TopDocs> topDocsPerSubQuery) {
@@ -123,30 +120,16 @@ private void updateQueryTopDocsWithCombinedScores(
         final Map<Integer, Float> combinedNormalizedScoresByDocId,
         final List<Integer> sortedScores
     ) {
-        // - count max number of hits among sub-queries
-        int maxHits = getMaxHits(topDocsPerSubQuery);
+        // - max number of hits will be the same which are passed from QueryPhase
+        long maxHits = compoundQueryTopDocs.getTotalHits().value;
         // - update query search results with normalized scores
         compoundQueryTopDocs.setScoreDocs(
             getCombinedScoreDocs(compoundQueryTopDocs, combinedNormalizedScoresByDocId, sortedScores, maxHits)
         );
         compoundQueryTopDocs.setTotalHits(getTotalHits(topDocsPerSubQuery, maxHits));
     }
 
-    /**
-     * Get max hits as number of unique doc ids from results of all sub-queries
-     * @param topDocsPerSubQuery list of topDocs objects for one shard
-     * @return number of unique doc ids
-     */
-    protected int getMaxHits(final List<TopDocs> topDocsPerSubQuery) {
-        Set<Integer> docIds = topDocsPerSubQuery.stream()
-            .filter(topDocs -> Objects.nonNull(topDocs.scoreDocs))
-            .flatMap(topDocs -> Arrays.stream(topDocs.scoreDocs))
-            .map(scoreDoc -> scoreDoc.doc)
-            .collect(Collectors.toSet());
-        return docIds.size();
-    }
-
-    private TotalHits getTotalHits(final List<TopDocs> topDocsPerSubQuery, int maxHits) {
+    private TotalHits getTotalHits(final List<TopDocs> topDocsPerSubQuery, final long maxHits) {
         TotalHits.Relation totalHits = TotalHits.Relation.EQUAL_TO;
         if (topDocsPerSubQuery.stream().anyMatch(topDocs -> topDocs.totalHits.relation == TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO)) {
             totalHits = TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO;

src/main/java/org/opensearch/neuralsearch/search/HybridTopScoreDocCollector.java

@@ -9,9 +9,8 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Objects;
-import java.util.stream.Collectors;
-import java.util.stream.IntStream;
 
+import lombok.Getter;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.Collector;
 import org.apache.lucene.search.HitQueue;
@@ -35,7 +34,9 @@ public class HybridTopScoreDocCollector implements Collector {
     private int docBase;
     private final HitsThresholdChecker hitsThresholdChecker;
     private TotalHits.Relation totalHitsRelation = TotalHits.Relation.EQUAL_TO;
-    private int[] totalHits;
+    @Getter
+    private int totalHits;
+    private int[] collectedHitsPerSubQuery;
     private final int numOfHits;
     private PriorityQueue<ScoreDoc>[] compoundScores;
 
@@ -94,23 +95,24 @@ public void collect(int doc) throws IOException {
                 if (Objects.isNull(compoundQueryScorer)) {
                     throw new IllegalArgumentException("scorers are null for all sub-queries in hybrid query");
                 }
-
                 float[] subScoresByQuery = compoundQueryScorer.hybridScores();
                 // iterate over results for each query
                 if (compoundScores == null) {
                     compoundScores = new PriorityQueue[subScoresByQuery.length];
                     for (int i = 0; i < subScoresByQuery.length; i++) {
                         compoundScores[i] = new HitQueue(numOfHits, false);
                     }
-                    totalHits = new int[subScoresByQuery.length];
+                    collectedHitsPerSubQuery = new int[subScoresByQuery.length];
                 }
+                // Increment total hit count which represents unique doc found on the shard
+                totalHits++;
                 for (int i = 0; i < subScoresByQuery.length; i++) {
                     float score = subScoresByQuery[i];
                     // if score is 0.0 there is no hits for that sub-query
                     if (score == 0) {
                         continue;
                     }
-                    totalHits[i]++;
+                    collectedHitsPerSubQuery[i]++;
                     PriorityQueue<ScoreDoc> pq = compoundScores[i];
                     ScoreDoc currentDoc = new ScoreDoc(doc + docBase, score);
                     // this way we're inserting into heap and do nothing else unless we reach the capacity
@@ -134,9 +136,17 @@ public List<TopDocs> topDocs() {
         if (compoundScores == null) {
             return new ArrayList<>();
         }
-        final List<TopDocs> topDocs = IntStream.range(0, compoundScores.length)
-            .mapToObj(i -> topDocsPerQuery(0, Math.min(totalHits[i], compoundScores[i].size()), compoundScores[i], totalHits[i]))
-            .collect(Collectors.toList());
+        final List<TopDocs> topDocs = new ArrayList<>();
+        for (int i = 0; i < compoundScores.length; i++) {
+            topDocs.add(
+                topDocsPerQuery(
+                    0,
+                    Math.min(collectedHitsPerSubQuery[i], compoundScores[i].size()),
+                    compoundScores[i],
+                    collectedHitsPerSubQuery[i]
+                )
+            );
+        }
         return topDocs;
     }
 

src/main/java/org/opensearch/neuralsearch/search/query/HybridCollectorManager.java

@@ -31,11 +31,8 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
-import java.util.Set;
-import java.util.stream.Collectors;
 
 import static org.opensearch.neuralsearch.search.util.HybridSearchResultFormatUtil.createDelimiterElementForHybridSearchResults;
 import static org.opensearch.neuralsearch.search.util.HybridSearchResultFormatUtil.createStartStopElementForHybridSearchResults;
@@ -145,7 +142,10 @@ public ReduceableSearchResult reduce(Collection<Collector> collectors) {
                 .findFirst()
                 .orElseThrow(() -> new IllegalStateException("cannot collect results of hybrid search query"));
             List<TopDocs> topDocs = hybridTopScoreDocCollector.topDocs();
-            TopDocs newTopDocs = getNewTopDocs(getTotalHits(this.trackTotalHitsUpTo, topDocs, isSingleShard), topDocs);
+            TopDocs newTopDocs = getNewTopDocs(
+                getTotalHits(this.trackTotalHitsUpTo, topDocs, isSingleShard, hybridTopScoreDocCollector.getTotalHits()),
+                topDocs
+            );
             float maxScore = getMaxScore(topDocs);
             TopDocsAndMaxScore topDocsAndMaxScore = new TopDocsAndMaxScore(newTopDocs, maxScore);
             return (QuerySearchResult result) -> { result.topDocs(topDocsAndMaxScore, getSortValueFormats(sortAndFormats)); };
@@ -196,24 +196,19 @@ private TopDocs getNewTopDocs(final TotalHits totalHits, final List<TopDocs> top
         return new TopDocs(totalHits, scoreDocs);
     }
 
-    private TotalHits getTotalHits(int trackTotalHitsUpTo, final List<TopDocs> topDocs, final boolean isSingleShard) {
+    private TotalHits getTotalHits(
+        int trackTotalHitsUpTo,
+        final List<TopDocs> topDocs,
+        final boolean isSingleShard,
+        final long maxTotalHits
+    ) {
         final TotalHits.Relation relation = trackTotalHitsUpTo == SearchContext.TRACK_TOTAL_HITS_DISABLED
             ? TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO
             : TotalHits.Relation.EQUAL_TO;
         if (topDocs == null || topDocs.isEmpty()) {
             return new TotalHits(0, relation);
         }
 
-        List<ScoreDoc[]> scoreDocs = topDocs.stream()
-            .map(topdDoc -> topdDoc.scoreDocs)
-            .filter(Objects::nonNull)
-            .collect(Collectors.toList());
-        Set<Integer> uniqueDocIds = new HashSet<>();
-        for (ScoreDoc[] scoreDocsArray : scoreDocs) {
-            uniqueDocIds.addAll(Arrays.stream(scoreDocsArray).map(scoreDoc -> scoreDoc.doc).collect(Collectors.toList()));
-        }
-        long maxTotalHits = uniqueDocIds.size();
-
         return new TotalHits(maxTotalHits, relation);
     }
 

src/test/java/org/opensearch/neuralsearch/processor/ScoreCombinationTechniqueTests.java

@@ -27,7 +27,7 @@ public void testCombination_whenMultipleSubqueriesResultsAndDefaultMethod_thenSc
 
         final List<CompoundTopDocs> queryTopDocs = List.of(
             new CompoundTopDocs(
-                new TotalHits(3, TotalHits.Relation.EQUAL_TO),
+                new TotalHits(5, TotalHits.Relation.EQUAL_TO),
                 List.of(
                     new TopDocs(
                         new TotalHits(3, TotalHits.Relation.EQUAL_TO),

src/test/java/org/opensearch/neuralsearch/query/HybridQueryIT.java

@@ -177,6 +177,35 @@ public void testComplexQuery_whenMultipleSubqueries_thenSuccessful() {
         }
     }
 
+    @SneakyThrows
+    public void testTotalHits_whenResultSizeIsLessThenDefaultSize_thenSuccessful() {
+        initializeIndexIfNotExist(TEST_BASIC_VECTOR_DOC_FIELD_INDEX_NAME);
+        createSearchPipelineWithResultsPostProcessor(SEARCH_PIPELINE);
+        TermQueryBuilder termQueryBuilder1 = QueryBuilders.termQuery(TEST_TEXT_FIELD_NAME_1, TEST_QUERY_TEXT3);
+        TermQueryBuilder termQueryBuilder2 = QueryBuilders.termQuery(TEST_TEXT_FIELD_NAME_1, TEST_QUERY_TEXT4);
+        TermQueryBuilder termQueryBuilder3 = QueryBuilders.termQuery(TEST_TEXT_FIELD_NAME_1, TEST_QUERY_TEXT5);
+        BoolQueryBuilder boolQueryBuilder = new BoolQueryBuilder();
+        boolQueryBuilder.should(termQueryBuilder2).should(termQueryBuilder3);
+
+        HybridQueryBuilder hybridQueryBuilderNeuralThenTerm = new HybridQueryBuilder();
+        hybridQueryBuilderNeuralThenTerm.add(termQueryBuilder1);
+        hybridQueryBuilderNeuralThenTerm.add(boolQueryBuilder);
+        Map<String, Object> searchResponseAsMap = search(
+            TEST_BASIC_VECTOR_DOC_FIELD_INDEX_NAME,
+            hybridQueryBuilderNeuralThenTerm,
+            null,
+            1,
+            Map.of("search_pipeline", SEARCH_PIPELINE)
+        );
+
+        assertEquals(1, getHitCount(searchResponseAsMap));
+        Map<String, Object> total = getTotalHits(searchResponseAsMap);
+        assertNotNull(total.get("value"));
+        assertEquals(3, total.get("value"));
+        assertNotNull(total.get("relation"));
+        assertEquals(RELATION_EQUAL_TO, total.get("relation"));
+    }
+
     /**
      * Tests complex query with multiple nested sub-queries, where some sub-queries are same
      * {

src/test/java/org/opensearch/neuralsearch/search/HybridTopScoreDocCollectorTests.java

@@ -4,6 +4,16 @@
  */
 package org.opensearch.neuralsearch.search;
 
+import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.search.LeafCollector;
+import org.apache.lucene.search.MatchAllDocsQuery;
+import org.apache.lucene.search.MatchNoDocsQuery;
+import org.apache.lucene.search.Scorable;
+import org.apache.lucene.search.ScoreDoc;
+import org.apache.lucene.search.ScoreMode;
+import org.apache.lucene.search.Scorer;
+import org.apache.lucene.search.TopDocs;
+import org.apache.lucene.search.Weight;
 import static org.apache.lucene.search.DocIdSetIterator.NO_MORE_DOCS;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
@@ -13,6 +23,9 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+import java.util.HashSet;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
@@ -24,16 +37,6 @@
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.search.DocIdSetIterator;
-import org.apache.lucene.search.LeafCollector;
-import org.apache.lucene.search.MatchAllDocsQuery;
-import org.apache.lucene.search.MatchNoDocsQuery;
-import org.apache.lucene.search.Scorable;
-import org.apache.lucene.search.ScoreDoc;
-import org.apache.lucene.search.ScoreMode;
-import org.apache.lucene.search.Scorer;
-import org.apache.lucene.search.TopDocs;
-import org.apache.lucene.search.Weight;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.tests.analysis.MockAnalyzer;
 import org.opensearch.index.mapper.TextFieldMapper;
@@ -50,6 +53,7 @@ public class HybridTopScoreDocCollectorTests extends OpenSearchQueryTestCase {
     private static final String TEST_QUERY_TEXT = "greeting";
     private static final String TEST_QUERY_TEXT2 = "salute";
     private static final int NUM_DOCS = 4;
+    private static final int NUM_HITS = 1;
     private static final int TOTAL_HITS_UP_TO = 1000;
 
     private static final int DOC_ID_1 = RandomUtils.nextInt(0, 100_000);
@@ -493,4 +497,71 @@ public void testCompoundScorer_whenHybridScorerIsTopLevelScorer_thenSuccessful()
         reader.close();
         directory.close();
     }
+
+    @SneakyThrows
+    public void testTotalHitsCountValidation_whenTotalHitsCollectedAtTopLevelInCollector_thenSuccessful() {
+        final Directory directory = newDirectory();
+        final IndexWriter w = new IndexWriter(directory, newIndexWriterConfig(new MockAnalyzer(random())));
+        FieldType ft = new FieldType(TextField.TYPE_NOT_STORED);
+        ft.setIndexOptions(random().nextBoolean() ? IndexOptions.DOCS : IndexOptions.DOCS_AND_FREQS);
+        ft.setOmitNorms(random().nextBoolean());
+        ft.freeze();
+
+        w.addDocument(getDocument(TEXT_FIELD_NAME, DOC_ID_1, FIELD_1_VALUE, ft));
+        w.addDocument(getDocument(TEXT_FIELD_NAME, DOC_ID_2, FIELD_2_VALUE, ft));
+        w.addDocument(getDocument(TEXT_FIELD_NAME, DOC_ID_3, FIELD_3_VALUE, ft));
+        w.addDocument(getDocument(TEXT_FIELD_NAME, DOC_ID_4, FIELD_4_VALUE, ft));
+        w.commit();
+
+        DirectoryReader reader = DirectoryReader.open(w);
+
+        LeafReaderContext leafReaderContext = reader.getContext().leaves().get(0);
+
+        HybridTopScoreDocCollector hybridTopScoreDocCollector = new HybridTopScoreDocCollector(
+            NUM_HITS,
+            new HitsThresholdChecker(Integer.MAX_VALUE)
+        );
+        LeafCollector leafCollector = hybridTopScoreDocCollector.getLeafCollector(leafReaderContext);
+        assertNotNull(leafCollector);
+
+        Weight weight = mock(Weight.class);
+        int[] docIdsForQuery1 = new int[] { DOC_ID_1, DOC_ID_2 };
+        Arrays.sort(docIdsForQuery1);
+        int[] docIdsForQuery2 = new int[] { DOC_ID_3, DOC_ID_4 };
+        Arrays.sort(docIdsForQuery2);
+        final List<Float> scores = Stream.generate(() -> random().nextFloat()).limit(NUM_DOCS).collect(Collectors.toList());
+        HybridQueryScorer hybridQueryScorer = new HybridQueryScorer(
+            weight,
+            Arrays.asList(
+                scorer(docIdsForQuery1, scores, fakeWeight(new MatchAllDocsQuery())),
+                scorer(docIdsForQuery2, scores, fakeWeight(new MatchAllDocsQuery()))
+            )
+        );
+
+        leafCollector.setScorer(hybridQueryScorer);
+        DocIdSetIterator iterator = hybridQueryScorer.iterator();
+        int nextDoc = iterator.nextDoc();
+        while (nextDoc != NO_MORE_DOCS) {
+            leafCollector.collect(nextDoc);
+            nextDoc = iterator.nextDoc();
+        }
+
+        List<TopDocs> topDocs = hybridTopScoreDocCollector.topDocs();
+        long totalHits = hybridTopScoreDocCollector.getTotalHits();
+        List<ScoreDoc[]> scoreDocs = topDocs.stream()
+            .map(topdDoc -> topdDoc.scoreDocs)
+            .filter(Objects::nonNull)
+            .collect(Collectors.toList());
+        Set<Integer> uniqueDocIds = new HashSet<>();
+        for (ScoreDoc[] scoreDocsArray : scoreDocs) {
+            uniqueDocIds.addAll(Arrays.stream(scoreDocsArray).map(scoreDoc -> scoreDoc.doc).collect(Collectors.toList()));
+        }
+        long maxTotalHits = uniqueDocIds.size();
+        assertEquals(4, totalHits);
+        // Total unique docs on the shard will be 2 as per 1 per sub-query
+        assertEquals(2, maxTotalHits);
+        w.close();
+        reader.close();
+        directory.close();
+    }
 }

src/test/java/org/opensearch/neuralsearch/search/query/HybridQueryPhaseSearcherTests.java

@@ -1025,7 +1025,9 @@ private static IndexMetadata getIndexMetadata() {
             RemoteStoreEnums.PathType.NAME,
             HASHED_PREFIX.name(),
             RemoteStoreEnums.PathHashAlgorithm.NAME,
-            RemoteStoreEnums.PathHashAlgorithm.FNV_1A_BASE64.name()
+            RemoteStoreEnums.PathHashAlgorithm.FNV_1A_BASE64.name(),
+            IndexMetadata.TRANSLOG_METADATA_KEY,
+            "false"
         );
         Settings idxSettings = Settings.builder()
             .put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT)