Add check to directly use ANN Search when filters match all docs.

CHANGELOG.md

@@ -23,6 +23,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Introduced a writing layer in native engines where relies on the writing interface to process IO. (#2241)[https://github.com/opensearch-project/k-NN/pull/2241]
 - Allow method parameter override for training based indices (#2290) https://github.com/opensearch-project/k-NN/pull/2290]
 - Optimizes lucene query execution to prevent unnecessary rewrites (#2305)[https://github.com/opensearch-project/k-NN/pull/2305]
+- Add check to directly use ANN Search when filters match all docs. (#2320)[https://github.com/opensearch-project/k-NN/pull/2320]
 ### Bug Fixes
 * Fixing the bug when a segment has no vector field present for disk based vector search (#2282)[https://github.com/opensearch-project/k-NN/pull/2282]
 * Allow validation for non knn index only after 2.17.0 (#2315)[https://github.com/opensearch-project/k-NN/pull/2315]

src/main/java/org/opensearch/knn/index/query/KNNWeight.java

@@ -129,6 +129,7 @@ public Scorer scorer(LeafReaderContext context) throws IOException {
      */
     public PerLeafResult searchLeaf(LeafReaderContext context, int k) throws IOException {
         final BitSet filterBitSet = getFilteredDocsBitSet(context);
+        final int maxDoc = context.reader().maxDoc();
         int cardinality = filterBitSet.cardinality();
         // We don't need to go to JNI layer if no documents are found which satisfy the filters
         // We should give this condition a deeper look that where it should be placed. For now I feel this is a good
@@ -145,6 +146,12 @@ public PerLeafResult searchLeaf(LeafReaderContext context, int k) throws IOExcep
             Map<Integer, Float> result = doExactSearch(context, new BitSetIterator(filterBitSet, cardinality), cardinality, k);
             return new PerLeafResult(filterWeight == null ? null : filterBitSet, result);
         }
+        /*
+         * If filters match all docs in this segment, then there is no need to do any extra step
+         * and should directly do ANN Search*/
+        if (filterWeight != null && cardinality == maxDoc) {
+            return new PerLeafResult(new FixedBitSet(0), doANNSearch(context, new FixedBitSet(0), 0, k));
+        }
         Map<Integer, Float> docIdsToScoreMap = doANNSearch(context, filterBitSet, cardinality, k);
         // See whether we have to perform exact search based on approx search results
         // This is required if there are no native engine files or if approximate search returned
@@ -320,6 +327,7 @@ private Map<Integer, Float> doANNSearch(
         // Now that we have the allocation, we need to readLock it
         indexAllocation.readLock();
         indexAllocation.incRef();
+
         try {
             if (indexAllocation.isClosed()) {
                 throw new RuntimeException("Index has already been closed");

src/test/java/org/opensearch/knn/index/query/KNNWeightTests.java

@@ -671,7 +671,7 @@ public void validateANNWithFilterQuery_whenDoingANN_thenSuccess(final boolean is
         when(liveDocsBits.length()).thenReturn(1000);
 
         final SegmentReader reader = mockSegmentReader();
-        when(reader.maxDoc()).thenReturn(filterDocIds.length);
+        when(reader.maxDoc()).thenReturn(filterDocIds.length + 1);
         when(reader.getLiveDocs()).thenReturn(liveDocsBits);
 
         final LeafReaderContext leafReaderContext = mock(LeafReaderContext.class);
@@ -758,6 +758,97 @@ public void validateANNWithFilterQuery_whenDoingANN_thenSuccess(final boolean is
         assertTrue(Comparators.isInOrder(actualDocIds, Comparator.naturalOrder()));
     }
 
+    @SneakyThrows
+    public void testANNWithFilterQuery_whenFiltersMatchAllDocs_thenSuccess() {
+        // Given
+        int k = 3;
+        final int[] filterDocIds = new int[] { 0, 1, 2, 3, 4, 5 };
+        FixedBitSet filterBitSet = new FixedBitSet(filterDocIds.length);
+        for (int docId : filterDocIds) {
+            filterBitSet.set(docId);
+        }
+
+        jniServiceMockedStatic.when(
+            () -> JNIService.queryIndex(
+                anyLong(),
+                eq(QUERY_VECTOR),
+                eq(k),
+                eq(HNSW_METHOD_PARAMETERS),
+                any(),
+                eq(new FixedBitSet(0).getBits()),
+                anyInt(),
+                any()
+            )
+        ).thenReturn(getFilteredKNNQueryResults());
+
+        final Bits liveDocsBits = mock(Bits.class);
+        for (int filterDocId : filterDocIds) {
+            when(liveDocsBits.get(filterDocId)).thenReturn(true);
+        }
+        when(liveDocsBits.length()).thenReturn(1000);
+
+        final SegmentReader reader = mockSegmentReader();
+        when(reader.maxDoc()).thenReturn(filterDocIds.length);
+        when(reader.getLiveDocs()).thenReturn(liveDocsBits);
+
+        final LeafReaderContext leafReaderContext = mock(LeafReaderContext.class);
+        when(leafReaderContext.reader()).thenReturn(reader);
+
+        final KNNQuery query = KNNQuery.builder()
+            .field(FIELD_NAME)
+            .queryVector(QUERY_VECTOR)
+            .k(k)
+            .indexName(INDEX_NAME)
+            .filterQuery(FILTER_QUERY)
+            .methodParameters(HNSW_METHOD_PARAMETERS)
+            .build();
+
+        final Weight filterQueryWeight = mock(Weight.class);
+        final Scorer filterScorer = mock(Scorer.class);
+        when(filterQueryWeight.scorer(leafReaderContext)).thenReturn(filterScorer);
+        // Just to make sure that we are not hitting the exact search condition
+        when(filterScorer.iterator()).thenReturn(DocIdSetIterator.all(filterDocIds.length + 1));
+
+        final float boost = (float) randomDoubleBetween(0, 10, true);
+        final KNNWeight knnWeight = new KNNWeight(query, boost, filterQueryWeight);
+
+        final FieldInfos fieldInfos = mock(FieldInfos.class);
+        final FieldInfo fieldInfo = mock(FieldInfo.class);
+        final Map<String, String> attributesMap = ImmutableMap.of(
+            KNN_ENGINE,
+            KNNEngine.FAISS.getName(),
+            SPACE_TYPE,
+            SpaceType.L2.getValue()
+        );
+
+        when(reader.getFieldInfos()).thenReturn(fieldInfos);
+        when(fieldInfos.fieldInfo(any())).thenReturn(fieldInfo);
+        when(fieldInfo.attributes()).thenReturn(attributesMap);
+
+        // When
+        final KNNScorer knnScorer = (KNNScorer) knnWeight.scorer(leafReaderContext);
+
+        // Then
+        assertNotNull(knnScorer);
+        final DocIdSetIterator docIdSetIterator = knnScorer.iterator();
+        assertNotNull(docIdSetIterator);
+        assertEquals(FILTERED_DOC_ID_TO_SCORES.size(), docIdSetIterator.cost());
+
+        jniServiceMockedStatic.verify(
+            () -> JNIService.queryIndex(anyLong(), eq(QUERY_VECTOR), eq(k), eq(HNSW_METHOD_PARAMETERS), any(), any(), anyInt(), any()),
+            times(1)
+        );
+
+        final List<Integer> actualDocIds = new ArrayList<>();
+        final Map<Integer, Float> translatedScores = getTranslatedScores(SpaceType.L2::scoreTranslation);
+        for (int docId = docIdSetIterator.nextDoc(); docId != NO_MORE_DOCS; docId = docIdSetIterator.nextDoc()) {
+            actualDocIds.add(docId);
+            assertEquals(translatedScores.get(docId) * boost, knnScorer.score(), 0.01f);
+        }
+        assertEquals(docIdSetIterator.cost(), actualDocIds.size());
+        assertTrue(Comparators.isInOrder(actualDocIds, Comparator.naturalOrder()));
+    }
+
     private SegmentReader mockSegmentReader() {
         Path path = mock(Path.class);
 
@@ -815,7 +906,7 @@ public void validateANNWithFilterQuery_whenExactSearch_thenSuccess(final boolean
             when(filterQueryWeight.scorer(leafReaderContext)).thenReturn(filterScorer);
             // scorer will return 2 documents
             when(filterScorer.iterator()).thenReturn(DocIdSetIterator.all(1));
-            when(reader.maxDoc()).thenReturn(1);
+            when(reader.maxDoc()).thenReturn(2);
             final Bits liveDocsBits = mock(Bits.class);
             when(reader.getLiveDocs()).thenReturn(liveDocsBits);
             when(liveDocsBits.get(filterDocId)).thenReturn(true);
@@ -891,6 +982,7 @@ public void testRadialSearch_whenNoEngineFiles_thenPerformExactSearch() {
         final LeafReaderContext leafReaderContext = mock(LeafReaderContext.class);
         final SegmentReader reader = mock(SegmentReader.class);
         when(leafReaderContext.reader()).thenReturn(reader);
+        when(reader.maxDoc()).thenReturn(1);
 
         final FSDirectory directory = mock(FSDirectory.class);
         when(reader.directory()).thenReturn(directory);
@@ -968,7 +1060,7 @@ public void testANNWithFilterQuery_whenExactSearchAndThresholdComputations_thenS
         when(filterQueryWeight.scorer(leafReaderContext)).thenReturn(filterScorer);
         // scorer will return 2 documents
         when(filterScorer.iterator()).thenReturn(DocIdSetIterator.all(1));
-        when(reader.maxDoc()).thenReturn(1);
+        when(reader.maxDoc()).thenReturn(2);
         final Bits liveDocsBits = mock(Bits.class);
         when(reader.getLiveDocs()).thenReturn(liveDocsBits);
         when(liveDocsBits.get(filterDocId)).thenReturn(true);
@@ -1168,6 +1260,7 @@ public void testANNWithFilterQuery_whenEmptyFilterIds_thenReturnEarly() {
         final LeafReaderContext leafReaderContext = mock(LeafReaderContext.class);
         final SegmentReader reader = mock(SegmentReader.class);
         when(leafReaderContext.reader()).thenReturn(reader);
+        when(reader.maxDoc()).thenReturn(1);
 
         final Weight filterQueryWeight = mock(Weight.class);
         final Scorer filterScorer = mock(Scorer.class);
@@ -1202,7 +1295,7 @@ public void testANNWithParentsFilter_whenExactSearch_thenSuccess() {
         // We will have 0, 1 for filteredIds and 2 will be the parent id for both of them
         final Scorer filterScorer = mock(Scorer.class);
         when(filterScorer.iterator()).thenReturn(DocIdSetIterator.all(2));
-        when(reader.maxDoc()).thenReturn(2);
+        when(reader.maxDoc()).thenReturn(3);
 
         // Query vector is {1.8f, 2.4f}, therefore, second vector {1.9f, 2.5f} should be returned in a result
         final List<float[]> vectors = Arrays.asList(new float[] { 0.1f, 0.3f }, new float[] { 1.9f, 2.5f });