GPU: Restrict GPU indexing to FLOAT element types (#139084)

Reject BYTE, BFLOAT16, and BIT element types in GPUPlugin by  returning
null, falling back to CPU-based vector indexing.

Author: mayya-sharipova

docs/changelog/139084.yaml

@@ -0,0 +1,5 @@
+pr: 139084
+summary: "GPU: Restrict GPU indexing to FLOAT element types"
+area: Vector Search
+type: enhancement
+issues: []

x-pack/plugin/gpu/src/internalClusterTest/java/org/elasticsearch/xpack/gpu/GPUPluginInitializationWithGPUIT.java

@@ -97,7 +97,6 @@ public void testAutoModeSupportedVectorType() {
             settings,
             indexOptions,
             randomGPUSupportedSimilarity(indexOptions.getType()),
-            // TODO add other type support
             DenseVectorFieldMapper.ElementType.FLOAT
         );
         assertNotNull(format);
@@ -118,12 +117,36 @@ public void testAutoModeUnsupportedVectorType() {
             settings,
             indexOptions,
             randomGPUSupportedSimilarity(indexOptions.getType()),
-            // TODO add other type support
             DenseVectorFieldMapper.ElementType.FLOAT
         );
         assertNull(format);
     }
 
+    public void testAutoModeUnsupportedElementType() {
+        gpuMode = GPUPlugin.GpuMode.AUTO;
+        assumeTrue("GPU_FORMAT feature flag enabled", GPUPlugin.GPU_FORMAT.isEnabled());
+
+        GPUPlugin gpuPlugin = internalCluster().getInstance(TestGPUPlugin.class);
+        VectorsFormatProvider vectorsFormatProvider = gpuPlugin.getVectorsFormatProvider();
+
+        createIndex("index1");
+        IndexSettings settings = getIndexSettings();
+        final var indexOptions = DenseVectorFieldTypeTests.randomGpuSupportedIndexOptions();
+        final var unsupportedElementType = randomFrom(
+            DenseVectorFieldMapper.ElementType.BYTE,
+            DenseVectorFieldMapper.ElementType.BFLOAT16,
+            DenseVectorFieldMapper.ElementType.BIT
+        );
+
+        var format = vectorsFormatProvider.getKnnVectorsFormat(
+            settings,
+            indexOptions,
+            randomGPUSupportedSimilarity(indexOptions.getType()),
+            unsupportedElementType
+        );
+        assertNull(format);
+    }
+
     public void testAutoModeLicenseNotSupported() {
         gpuMode = GPUPlugin.GpuMode.AUTO;
         isGpuIndexingFeatureAllowed = false;
@@ -140,7 +163,6 @@ public void testAutoModeLicenseNotSupported() {
             settings,
             indexOptions,
             randomGPUSupportedSimilarity(indexOptions.getType()),
-            // TODO add other type support
             DenseVectorFieldMapper.ElementType.FLOAT
         );
         assertNull(format);
@@ -162,7 +184,6 @@ public void testTrueModeSupportedVectorType() {
             settings,
             indexOptions,
             randomGPUSupportedSimilarity(indexOptions.getType()),
-            // TODO add other type support
             DenseVectorFieldMapper.ElementType.FLOAT
         );
         assertNotNull(format);
@@ -183,12 +204,36 @@ public void testTrueModeUnsupportedVectorType() {
             settings,
             indexOptions,
             randomGPUSupportedSimilarity(indexOptions.getType()),
-            // TODO add other type support
             DenseVectorFieldMapper.ElementType.FLOAT
         );
         assertNull(format);
     }
 
+    public void testTrueModeUnsupportedElementType() {
+        gpuMode = GPUPlugin.GpuMode.TRUE;
+        assumeTrue("GPU_FORMAT feature flag enabled", GPUPlugin.GPU_FORMAT.isEnabled());
+
+        GPUPlugin gpuPlugin = internalCluster().getInstance(TestGPUPlugin.class);
+        VectorsFormatProvider vectorsFormatProvider = gpuPlugin.getVectorsFormatProvider();
+
+        createIndex("index1");
+        IndexSettings settings = getIndexSettings();
+        final var indexOptions = DenseVectorFieldTypeTests.randomGpuSupportedIndexOptions();
+        final var unsupportedElementType = randomFrom(
+            DenseVectorFieldMapper.ElementType.BYTE,
+            DenseVectorFieldMapper.ElementType.BFLOAT16,
+            DenseVectorFieldMapper.ElementType.BIT
+        );
+
+        var format = vectorsFormatProvider.getKnnVectorsFormat(
+            settings,
+            indexOptions,
+            randomGPUSupportedSimilarity(indexOptions.getType()),
+            unsupportedElementType
+        );
+        assertNull(format);
+    }
+
     public void testTrueModeLicenseNotSupported() {
         gpuMode = GPUPlugin.GpuMode.TRUE;
         isGpuIndexingFeatureAllowed = false;
@@ -205,7 +250,6 @@ public void testTrueModeLicenseNotSupported() {
             settings,
             indexOptions,
             randomGPUSupportedSimilarity(indexOptions.getType()),
-            // TODO add other type support
             DenseVectorFieldMapper.ElementType.FLOAT
         );
         assertNull(format);
@@ -227,7 +271,6 @@ public void testFalseModeNeverUsesGpu() {
             settings,
             indexOptions,
             randomGPUSupportedSimilarity(indexOptions.getType()),
-            // TODO add other type support
             DenseVectorFieldMapper.ElementType.FLOAT
         );
         assertNull(format);

x-pack/plugin/gpu/src/main/java/org/elasticsearch/xpack/gpu/GPUPlugin.java

@@ -117,15 +117,21 @@ public VectorsFormatProvider getVectorsFormatProvider() {
         return (indexSettings, indexOptions, similarity, elementType) -> {
             if (GPU_FORMAT.isEnabled() && isGpuIndexingFeatureAllowed()) {
                 if ((gpuMode == GpuMode.TRUE || (gpuMode == GpuMode.AUTO && GPUSupport.isSupported()))
-                    && vectorIndexTypeSupported(indexOptions.getType())) {
+                    && vectorIndexAndElementTypeSupported(indexOptions.getType(), elementType)) {
                     return getVectorsFormat(indexOptions, similarity);
                 }
             }
             return null;
         };
     }
 
-    private boolean vectorIndexTypeSupported(DenseVectorFieldMapper.VectorIndexType type) {
+    private boolean vectorIndexAndElementTypeSupported(
+        DenseVectorFieldMapper.VectorIndexType type,
+        DenseVectorFieldMapper.ElementType elementType
+    ) {
+        if (elementType != DenseVectorFieldMapper.ElementType.FLOAT) {
+            return false;
+        }
         return type == DenseVectorFieldMapper.VectorIndexType.HNSW || type == DenseVectorFieldMapper.VectorIndexType.INT8_HNSW;
     }