addressing PR comments - fix for delayed dimensions provided when setting up a dense_vector field

Author: pmpailis

server/src/internalClusterTest/java/org/elasticsearch/index/mapper/DynamicMappingIT.java

@@ -914,8 +914,9 @@ public void testKnnSubObject() throws Exception {
     public void testDenseVectorDynamicMapping() throws Exception {
         assertAcked(indicesAdmin().prepareCreate("test").setMapping("""
             {
-            "dynamic": "true"
-            }""").get());
+                "dynamic": "true"
+            }
+            """).get());
 
         client().index(
             new IndexRequest("test").source("vector_int8", Randomness.get().doubles(BBQ_DIMS_DEFAULT_THRESHOLD - 1, 0.0, 5.0).toArray())
@@ -932,6 +933,35 @@ public void testDenseVectorDynamicMapping() throws Exception {
         assertTrue(new WriteField("properties.vector_int8.index_options.type", () -> mappings).get(null).toString().equals("int8_hnsw"));
         assertTrue(new WriteField("properties.vector_bbq", () -> mappings).exists());
         assertTrue(new WriteField("properties.vector_bbq.index_options.type", () -> mappings).get(null).toString().equals("bbq_hnsw"));
+    }
+
+    public void testBBQDynamicMappingWhenFirstIngestingDoc() throws Exception {
+        assertAcked(indicesAdmin().prepareCreate("test").setMapping("""
+            {
+                "properties": {
+                    "vector": {
+                        "type": "dense_vector"
+                    }
+                }
+            }
+            """).get());
 
+        Map<String, Object> mappings = indicesAdmin().prepareGetMappings(TEST_REQUEST_TIMEOUT, "test")
+            .get()
+            .mappings()
+            .get("test")
+            .sourceAsMap();
+        assertTrue(new WriteField("properties.vector", () -> mappings).exists());
+        assertFalse(new WriteField("properties.vector.index_options.type", () -> mappings).exists());
+
+        client().index(new IndexRequest("test").source("vector", Randomness.get().doubles(BBQ_DIMS_DEFAULT_THRESHOLD, 0.0, 5.0).toArray()))
+            .get();
+        Map<String, Object> updatedMappings = indicesAdmin().prepareGetMappings(TEST_REQUEST_TIMEOUT, "test")
+            .get()
+            .mappings()
+            .get("test")
+            .sourceAsMap();
+        assertTrue(new WriteField("properties.vector", () -> updatedMappings).exists());
+        assertTrue(new WriteField("properties.vector.index_options.type", () -> updatedMappings).get(null).toString().equals("bbq_hnsw"));
     }
 }

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

@@ -350,8 +350,8 @@ public Builder(String name, IndexVersion indexVersionCreated) {
         }
 
         private DenseVectorIndexOptions defaultIndexOptions(boolean defaultInt8Hnsw, boolean defaultBBQHnsw) {
-            if (elementType.getValue() == ElementType.FLOAT && this.indexed.getValue()) {
-                if (defaultBBQHnsw && this.dims != null && this.dims.isConfigured() && this.dims.getValue() >= BBQ_DIMS_DEFAULT_THRESHOLD) {
+            if (this.dims != null && this.dims.isConfigured() && elementType.getValue() == ElementType.FLOAT && this.indexed.getValue()) {
+                if (defaultBBQHnsw && this.dims.getValue() >= BBQ_DIMS_DEFAULT_THRESHOLD) {
                     return new BBQHnswIndexOptions(
                         Lucene99HnswVectorsFormat.DEFAULT_MAX_CONN,
                         Lucene99HnswVectorsFormat.DEFAULT_BEAM_WIDTH,
@@ -2713,8 +2713,29 @@ public void parse(DocumentParserContext context) throws IOException {
         }
         if (fieldType().dims == null) {
             int dims = fieldType().elementType.parseDimensionCount(context);
-            if (fieldType().indexOptions != null) {
-                fieldType().indexOptions.validateDimension(dims);
+            IndexVersion indexVersionCreated = context.indexSettings().getIndexVersionCreated();
+            final boolean defaultInt8Hnsw = indexVersionCreated.onOrAfter(IndexVersions.DEFAULT_DENSE_VECTOR_TO_INT8_HNSW);
+            final boolean defaultBBQ8Hnsw = indexVersionCreated.onOrAfter(IndexVersions.DEFAULT_DENSE_VECTOR_TO_BBQ_HNSW);
+            DenseVectorIndexOptions denseVectorIndexOptions = fieldType().indexOptions;
+            if (denseVectorIndexOptions == null && fieldType().getElementType() == ElementType.FLOAT && fieldType().isIndexed()) {
+                if (defaultBBQ8Hnsw && dims >= BBQ_DIMS_DEFAULT_THRESHOLD) {
+                    denseVectorIndexOptions = new BBQHnswIndexOptions(
+                        Lucene99HnswVectorsFormat.DEFAULT_MAX_CONN,
+                        Lucene99HnswVectorsFormat.DEFAULT_BEAM_WIDTH,
+                        new RescoreVector(DEFAULT_OVERSAMPLE)
+                    );
+                } else if (defaultInt8Hnsw) {
+                    denseVectorIndexOptions = new Int8HnswIndexOptions(
+                        Lucene99HnswVectorsFormat.DEFAULT_MAX_CONN,
+                        Lucene99HnswVectorsFormat.DEFAULT_BEAM_WIDTH,
+                        null,
+                        null
+                    );
+                }
+            }
+            ;
+            if (denseVectorIndexOptions != null) {
+                denseVectorIndexOptions.validateDimension(dims);
             }
             DenseVectorFieldType updatedDenseVectorFieldType = new DenseVectorFieldType(
                 fieldType().name(),
@@ -2723,15 +2744,15 @@ public void parse(DocumentParserContext context) throws IOException {
                 dims,
                 fieldType().indexed,
                 fieldType().similarity,
-                fieldType().indexOptions,
+                denseVectorIndexOptions,
                 fieldType().meta(),
                 fieldType().isSyntheticSource
             );
             Mapper update = new DenseVectorFieldMapper(
                 leafName(),
                 updatedDenseVectorFieldType,
                 builderParams,
-                indexOptions,
+                denseVectorIndexOptions,
                 indexCreatedVersion
             );
             context.addDynamicMapper(update);