Update Default value of Oversample for bbq (#127134)

* Unit test to validate default behavior

* adding default value to oversample for bbq

* Fix code style issue

* Update docs/changelog/127134.yaml

* Update changelog

* Adding index version to support only new indices

* Update index version name to better match

* Adding a simple yaml test to verify the yaml functionality for oversample value

* Refactor knn float to add rescore vector by default when index type is one of bbq

* adding yaml tests to verify oversampel default value

* Fixing format issue for not_exists

Author: Samiul-TheSoccerFan

docs/changelog/127134.yaml

@@ -0,0 +1,5 @@
+pr: 127134
+summary: Define a default oversample value for dense vectors with bbq_hnsw/bbq_flat
+area: Vector Search
+type: enhancement
+issues: []

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_bbq_hnsw.yml

@@ -568,3 +568,14 @@ setup:
   - match: { hits.hits.1._score: $default_rescore1 }
   - match: { hits.hits.2._score: $override_score2 }
   - match: { hits.hits.2._score: $default_rescore2 }
+
+---
+"default oversample value":
+  - requires:
+      cluster_features: ["mapper.dense_vector.default_oversample_value_for_bbq"]
+      reason: "Needs default_oversample_value_for_bbq feature"
+  - do:
+      indices.get_mapping:
+        index: bbq_hnsw
+
+  - match: { bbq_hnsw.mappings.properties.vector.index_options.rescore_vector.oversample: 3.0 }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_bbq_flat.yml

@@ -339,3 +339,14 @@ setup:
   - match: { hits.hits.0._score: $rescore_score0 }
   - match: { hits.hits.1._score: $rescore_score1 }
   - match: { hits.hits.2._score: $rescore_score2 }
+
+---
+"default oversample value":
+  - requires:
+      cluster_features: ["mapper.dense_vector.default_oversample_value_for_bbq"]
+      reason: "Needs default_oversample_value_for_bbq feature"
+  - do:
+      indices.get_mapping:
+        index: bbq_flat
+
+  - match: { bbq_flat.mappings.properties.vector.index_options.rescore_vector.oversample: 3.0 }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_int4_flat.yml

@@ -495,3 +495,14 @@ setup:
   - match: { hits.hits.0._score: $rescore_score0 }
   - match: { hits.hits.1._score: $rescore_score1 }
   - match: { hits.hits.2._score: $rescore_score2 }
+
+---
+"no default oversample value":
+  - requires:
+      cluster_features: ["mapper.dense_vector.default_oversample_value_for_bbq"]
+      reason: "Needs default_oversample_value_for_bbq feature"
+  - do:
+      indices.get_mapping:
+        index: int4_flat
+
+  - not_exists: int4_flat.mappings.properties.vector.index_options.rescore_vector

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_int8_flat.yml

@@ -436,3 +436,14 @@ setup:
   - match: { hits.hits.0._score: $rescore_score0 }
   - match: { hits.hits.1._score: $rescore_score1 }
   - match: { hits.hits.2._score: $rescore_score2 }
+
+---
+"no default oversample value":
+  - requires:
+      cluster_features: ["mapper.dense_vector.default_oversample_value_for_bbq"]
+      reason: "Needs default_oversample_value_for_bbq feature"
+  - do:
+      indices.get_mapping:
+        index: int8_flat
+
+  - not_exists: int8_flat.mappings.properties.vector.index_options.rescore_vector

server/src/main/java/org/elasticsearch/index/IndexVersions.java

@@ -161,6 +161,7 @@ private static Version parseUnchecked(String version) {
     public static final IndexVersion USE_LUCENE101_POSTINGS_FORMAT = def(9_021_0_00, Version.LUCENE_10_1_0);
     public static final IndexVersion UPGRADE_TO_LUCENE_10_2_0 = def(9_022_00_0, Version.LUCENE_10_2_0);
     public static final IndexVersion UPGRADE_TO_LUCENE_10_2_1 = def(9_023_00_0, Version.LUCENE_10_2_1);
+    public static final IndexVersion DEFAULT_OVERSAMPLE_VALUE_FOR_BBQ = def(9_024_0_00, Version.LUCENE_10_2_1);
     /*
      * STOP! READ THIS FIRST! No, really,
      *        ____ _____ ___  ____  _        ____  _____    _    ____    _____ _   _ ___ ____    _____ ___ ____  ____ _____ _

server/src/main/java/org/elasticsearch/index/mapper/MapperFeatures.java

@@ -16,6 +16,7 @@
 
 import static org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper.RESCORE_VECTOR_QUANTIZED_VECTOR_MAPPING;
 import static org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper.RESCORE_ZERO_VECTOR_QUANTIZED_VECTOR_MAPPING;
+import static org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper.USE_DEFAULT_OVERSAMPLE_VALUE_FOR_BBQ;
 
 /**
  * Spec for mapper-related features.
@@ -66,7 +67,8 @@ public Set<NodeFeature> getTestFeatures() {
             RESCORE_VECTOR_QUANTIZED_VECTOR_MAPPING,
             DateFieldMapper.INVALID_DATE_FIX,
             NPE_ON_DIMS_UPDATE_FIX,
-            RESCORE_ZERO_VECTOR_QUANTIZED_VECTOR_MAPPING
+            RESCORE_ZERO_VECTOR_QUANTIZED_VECTOR_MAPPING,
+            USE_DEFAULT_OVERSAMPLE_VALUE_FOR_BBQ
         );
     }
 }

server/src/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java

@@ -117,11 +117,15 @@ public static boolean isNotUnitVector(float magnitude) {
     public static final IndexVersion ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS = IndexVersions.ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS;
     public static final IndexVersion RESCORE_PARAMS_ALLOW_ZERO_TO_QUANTIZED_VECTORS =
         IndexVersions.RESCORE_PARAMS_ALLOW_ZERO_TO_QUANTIZED_VECTORS;
+    public static final IndexVersion DEFAULT_OVERSAMPLE_VALUE_FOR_BBQ = IndexVersions.DEFAULT_OVERSAMPLE_VALUE_FOR_BBQ;
 
     public static final NodeFeature RESCORE_VECTOR_QUANTIZED_VECTOR_MAPPING = new NodeFeature("mapper.dense_vector.rescore_vector");
     public static final NodeFeature RESCORE_ZERO_VECTOR_QUANTIZED_VECTOR_MAPPING = new NodeFeature(
         "mapper.dense_vector.rescore_zero_vector"
     );
+    public static final NodeFeature USE_DEFAULT_OVERSAMPLE_VALUE_FOR_BBQ = new NodeFeature(
+        "mapper.dense_vector.default_oversample_value_for_bbq"
+    );
 
     public static final String CONTENT_TYPE = "dense_vector";
     public static final short MAX_DIMS_COUNT = 4096; // maximum allowed number of dimensions
@@ -131,6 +135,7 @@ public static boolean isNotUnitVector(float magnitude) {
                                                                         // vector
     public static final int MAGNITUDE_BYTES = 4;
     public static final int OVERSAMPLE_LIMIT = 10_000; // Max oversample allowed
+    public static final float DEFAULT_OVERSAMPLE = 3.0F; // Default oversample value
 
     private static DenseVectorFieldMapper toType(FieldMapper in) {
         return (DenseVectorFieldMapper) in;
@@ -1462,6 +1467,9 @@ public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOpti
                 RescoreVector rescoreVector = null;
                 if (indexVersion.onOrAfter(ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)) {
                     rescoreVector = RescoreVector.fromIndexOptions(indexOptionsMap, indexVersion);
+                    if (rescoreVector == null && indexVersion.onOrAfter(DEFAULT_OVERSAMPLE_VALUE_FOR_BBQ)) {
+                        rescoreVector = new RescoreVector(DEFAULT_OVERSAMPLE);
+                    }
                 }
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
                 return new BBQHnswIndexOptions(m, efConstruction, rescoreVector);
@@ -1483,6 +1491,9 @@ public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOpti
                 RescoreVector rescoreVector = null;
                 if (indexVersion.onOrAfter(ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)) {
                     rescoreVector = RescoreVector.fromIndexOptions(indexOptionsMap, indexVersion);
+                    if (rescoreVector == null && indexVersion.onOrAfter(DEFAULT_OVERSAMPLE_VALUE_FOR_BBQ)) {
+                        rescoreVector = new RescoreVector(DEFAULT_OVERSAMPLE);
+                    }
                 }
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
                 return new BBQFlatIndexOptions(rescoreVector);
@@ -2311,6 +2322,10 @@ int getVectorDimensions() {
         ElementType getElementType() {
             return elementType;
         }
+
+        IndexOptions getIndexOptions() {
+            return indexOptions;
+        }
     }
 
     private final IndexOptions indexOptions;

server/src/test/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapperTests.java

@@ -1022,6 +1022,60 @@ public void testInvalidRescoreVector() {
         }
     }
 
+    public void testDefaultOversampleValue() throws IOException {
+        {
+            DocumentMapper mapperService = createDocumentMapper(fieldMapping(b -> {
+                b.field("type", "dense_vector");
+                b.field("dims", 128);
+                b.field("index", true);
+                b.field("similarity", "dot_product");
+                b.startObject("index_options");
+                b.field("type", "bbq_hnsw");
+                b.endObject();
+            }));
+
+            DenseVectorFieldMapper denseVectorFieldMapper = (DenseVectorFieldMapper) mapperService.mappers().getMapper("field");
+            DenseVectorFieldMapper.BBQHnswIndexOptions indexOptions = (DenseVectorFieldMapper.BBQHnswIndexOptions) denseVectorFieldMapper
+                .fieldType()
+                .getIndexOptions();
+            assertEquals(3.0F, indexOptions.rescoreVector.oversample(), 0.0F);
+        }
+        {
+            DocumentMapper mapperService = createDocumentMapper(fieldMapping(b -> {
+                b.field("type", "dense_vector");
+                b.field("dims", 128);
+                b.field("index", true);
+                b.field("similarity", "dot_product");
+                b.startObject("index_options");
+                b.field("type", "bbq_flat");
+                b.endObject();
+            }));
+
+            DenseVectorFieldMapper denseVectorFieldMapper = (DenseVectorFieldMapper) mapperService.mappers().getMapper("field");
+            DenseVectorFieldMapper.BBQFlatIndexOptions indexOptions = (DenseVectorFieldMapper.BBQFlatIndexOptions) denseVectorFieldMapper
+                .fieldType()
+                .getIndexOptions();
+            assertEquals(3.0F, indexOptions.rescoreVector.oversample(), 0.0F);
+        }
+        {
+            DocumentMapper mapperService = createDocumentMapper(fieldMapping(b -> {
+                b.field("type", "dense_vector");
+                b.field("dims", 128);
+                b.field("index", true);
+                b.field("similarity", "dot_product");
+                b.startObject("index_options");
+                b.field("type", "int8_hnsw");
+                b.endObject();
+            }));
+
+            DenseVectorFieldMapper denseVectorFieldMapper = (DenseVectorFieldMapper) mapperService.mappers().getMapper("field");
+            DenseVectorFieldMapper.Int8HnswIndexOptions indexOptions = (DenseVectorFieldMapper.Int8HnswIndexOptions) denseVectorFieldMapper
+                .fieldType()
+                .getIndexOptions();
+            assertNull(indexOptions.rescoreVector);
+        }
+    }
+
     public void testDims() {
         {
             Exception e = expectThrows(MapperParsingException.class, () -> createMapperService(fieldMapping(b -> {

server/src/test/java/org/elasticsearch/search/vectors/AbstractKnnVectorQueryBuilderTestCase.java

@@ -46,6 +46,7 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import static org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper.DEFAULT_OVERSAMPLE;
 import static org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper.OVERSAMPLE_LIMIT;
 import static org.elasticsearch.search.SearchService.DEFAULT_SIZE;
 import static org.hamcrest.Matchers.containsString;
@@ -144,7 +145,7 @@ protected KnnVectorQueryBuilder doCreateTestQueryBuilder() {
             fieldName,
             k,
             numCands,
-            randomRescoreVectorBuilder(),
+            isIndextypeBBQ() ? randomBBQRescoreVectorBuilder() : randomRescoreVectorBuilder(),
             randomFloat()
         );
 
@@ -161,6 +162,14 @@ protected KnnVectorQueryBuilder doCreateTestQueryBuilder() {
         return queryBuilder;
     }
 
+    private boolean isIndextypeBBQ() {
+        return indexType.equals("bbq_hnsw") || indexType.equals("bbq_flat");
+    }
+
+    protected RescoreVectorBuilder randomBBQRescoreVectorBuilder() {
+        return new RescoreVectorBuilder(randomBoolean() ? DEFAULT_OVERSAMPLE : randomFloatBetween(1.0f, 10.0f, false));
+    }
+
     protected RescoreVectorBuilder randomRescoreVectorBuilder() {
         if (randomBoolean()) {
             return null;