[Backport main] Remove skip building graph check for quantization use case

CHANGELOG.md

@@ -30,6 +30,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Add WithFieldName implementation to KNNQueryBuilder (#2398)[https://github.com/opensearch-project/k-NN/pull/2398]
 - Make the build work for M series MacOS without manual code changes and local JAVA_HOME config (#2397)[https://github.com/opensearch-project/k-NN/pull/2397]
 - Remove DocsWithFieldSet reference from NativeEngineFieldVectorsWriter (#2408)[https://github.com/opensearch-project/k-NN/pull/2408]
+- Remove skip building graph check for quantization use case (#2430)[https://github.com/opensearch-project/k-NN/2430]
 ### 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]
 * Fixing the bug where search fails with "fields" parameter for an index with a knn_vector field (#2314)[https://github.com/opensearch-project/k-NN/pull/2314]

src/main/java/org/opensearch/knn/index/codec/KNN990Codec/NativeEngines990KnnVectorsWriter.java

@@ -104,9 +104,8 @@ public void flush(int maxDoc, final Sorter.DocMap sortMap) throws IOException {
                 field.getVectors()
             );
             final QuantizationState quantizationState = train(field.getFieldInfo(), knnVectorValuesSupplier, totalLiveDocs);
-            // Check only after quantization state writer finish writing its state, since it is required
-            // even if there are no graph files in segment, which will be later used by exact search
-            if (shouldSkipBuildingVectorDataStructure(totalLiveDocs)) {
+            // should skip graph building only for non quantization use case and if threshold is met
+            if (quantizationState == null && shouldSkipBuildingVectorDataStructure(totalLiveDocs)) {
                 log.info(
                     "Skip building vector data structure for field: {}, as liveDoc: {} is less than the threshold {} during flush",
                     fieldInfo.name,
@@ -144,9 +143,8 @@ public void mergeOneField(final FieldInfo fieldInfo, final MergeState mergeState
         }
 
         final QuantizationState quantizationState = train(fieldInfo, knnVectorValuesSupplier, totalLiveDocs);
-        // Check only after quantization state writer finish writing its state, since it is required
-        // even if there are no graph files in segment, which will be later used by exact search
-        if (shouldSkipBuildingVectorDataStructure(totalLiveDocs)) {
+        // should skip graph building only for non quantization use case and if threshold is met
+        if (quantizationState == null && shouldSkipBuildingVectorDataStructure(totalLiveDocs)) {
             log.info(
                 "Skip building vector data structure for field: {}, as liveDoc: {} is less than the threshold {} during merge",
                 fieldInfo.name,

src/test/java/org/opensearch/knn/index/codec/KNN990Codec/NativeEngines990KnnVectorsWriterFlushTests.java

@@ -630,8 +630,7 @@ public void testFlush_whenThresholdIsEqualToFixedValue_thenRelevantNativeIndexWr
         }
     }
 
-    public void testFlush_whenQuantizationIsProvided_whenBuildGraphDatStructureThresholdIsNotMet_thenSkipBuildingGraph()
-        throws IOException {
+    public void testFlush_whenQuantizationIsProvided_whenBuildGraphDatStructureThresholdIsNotMet_thenStillBuildGraph() throws IOException {
         // Given
         List<KNNVectorValues<float[]>> expectedVectorValues = new ArrayList<>();
         final Map<Integer, Integer> sizeMap = new HashMap<>();
@@ -714,7 +713,6 @@ public void testFlush_whenQuantizationIsProvided_whenBuildGraphDatStructureThres
             } else {
                 assertEquals(0, knn990QuantWriterMockedConstruction.constructed().size());
             }
-            verifyNoInteractions(nativeIndexWriter);
             IntStream.range(0, vectorsPerField.size()).forEach(i -> {
                 try {
                     if (vectorsPerField.get(i).isEmpty()) {
@@ -729,12 +727,12 @@ public void testFlush_whenQuantizationIsProvided_whenBuildGraphDatStructureThres
             final Long expectedTimesGetVectorValuesIsCalled = vectorsPerField.stream().filter(Predicate.not(Map::isEmpty)).count();
             knnVectorValuesFactoryMockedStatic.verify(
                 () -> KNNVectorValuesFactory.getVectorValues(any(VectorDataType.class), any(DocsWithFieldSet.class), any()),
-                times(Math.toIntExact(expectedTimesGetVectorValuesIsCalled))
+                times(Math.toIntExact(expectedTimesGetVectorValuesIsCalled) * 2)
             );
         }
     }
 
-    public void testFlush_whenQuantizationIsProvided_whenBuildGraphDatStructureThresholdIsNegative_thenSkipBuildingGraph()
+    public void testFlush_whenQuantizationIsProvided_whenBuildGraphDatStructureThresholdIsNegative_thenStillBuildGraph()
         throws IOException {
         // Given
         List<KNNVectorValues<float[]>> expectedVectorValues = new ArrayList<>();
@@ -817,7 +815,6 @@ public void testFlush_whenQuantizationIsProvided_whenBuildGraphDatStructureThres
             } else {
                 assertEquals(0, knn990QuantWriterMockedConstruction.constructed().size());
             }
-            verifyNoInteractions(nativeIndexWriter);
             IntStream.range(0, vectorsPerField.size()).forEach(i -> {
                 try {
                     if (vectorsPerField.get(i).isEmpty()) {
@@ -832,7 +829,7 @@ public void testFlush_whenQuantizationIsProvided_whenBuildGraphDatStructureThres
             final Long expectedTimesGetVectorValuesIsCalled = vectorsPerField.stream().filter(Predicate.not(Map::isEmpty)).count();
             knnVectorValuesFactoryMockedStatic.verify(
                 () -> KNNVectorValuesFactory.getVectorValues(any(VectorDataType.class), any(DocsWithFieldSet.class), any()),
-                times(Math.toIntExact(expectedTimesGetVectorValuesIsCalled))
+                times(Math.toIntExact(expectedTimesGetVectorValuesIsCalled) * 2)
             );
         }
     }