[8.x] Support configurable chunking in semantic_text fields (#121041)

docs/changelog/121041.yaml

@@ -0,0 +1,5 @@
+pr: 121041
+summary: Support configurable chunking in `semantic_text` fields
+area: Relevance
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -202,6 +202,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion RERANK_COMMON_OPTIONS_ADDED_8_19 = def(8_841_0_15);
     public static final TransportVersion REMOTE_EXCEPTION_8_19 = def(8_841_0_16);
     public static final TransportVersion AMAZON_BEDROCK_TASK_SETTINGS_8_19 = def(8_841_0_17);
+    public static final TransportVersion SEMANTIC_TEXT_CHUNKING_CONFIG_8_19 = def(8_841_0_18);
 
     /*
      * STOP! READ THIS FIRST! No, really,

server/src/main/java/org/elasticsearch/cluster/metadata/InferenceFieldMetadata.java

@@ -12,6 +12,7 @@
 import org.elasticsearch.TransportVersions;
 import org.elasticsearch.cluster.Diff;
 import org.elasticsearch.cluster.SimpleDiffable;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.xcontent.ToXContentFragment;
@@ -22,8 +23,11 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 
+import static org.elasticsearch.TransportVersions.SEMANTIC_TEXT_CHUNKING_CONFIG_8_19;
+
 /**
  * Contains inference field data for fields.
  * As inference is done in the coordinator node to avoid re-doing it at shard / replica level, the coordinator needs to check for the need
@@ -35,21 +39,30 @@ public final class InferenceFieldMetadata implements SimpleDiffable<InferenceFie
     private static final String INFERENCE_ID_FIELD = "inference_id";
     private static final String SEARCH_INFERENCE_ID_FIELD = "search_inference_id";
     private static final String SOURCE_FIELDS_FIELD = "source_fields";
+    static final String CHUNKING_SETTINGS_FIELD = "chunking_settings";
 
     private final String name;
     private final String inferenceId;
     private final String searchInferenceId;
     private final String[] sourceFields;
+    private final Map<String, Object> chunkingSettings;
 
-    public InferenceFieldMetadata(String name, String inferenceId, String[] sourceFields) {
-        this(name, inferenceId, inferenceId, sourceFields);
+    public InferenceFieldMetadata(String name, String inferenceId, String[] sourceFields, Map<String, Object> chunkingSettings) {
+        this(name, inferenceId, inferenceId, sourceFields, chunkingSettings);
     }
 
-    public InferenceFieldMetadata(String name, String inferenceId, String searchInferenceId, String[] sourceFields) {
+    public InferenceFieldMetadata(
+        String name,
+        String inferenceId,
+        String searchInferenceId,
+        String[] sourceFields,
+        Map<String, Object> chunkingSettings
+    ) {
         this.name = Objects.requireNonNull(name);
         this.inferenceId = Objects.requireNonNull(inferenceId);
         this.searchInferenceId = Objects.requireNonNull(searchInferenceId);
         this.sourceFields = Objects.requireNonNull(sourceFields);
+        this.chunkingSettings = chunkingSettings != null ? Map.copyOf(chunkingSettings) : null;
     }
 
     public InferenceFieldMetadata(StreamInput input) throws IOException {
@@ -61,6 +74,11 @@ public InferenceFieldMetadata(StreamInput input) throws IOException {
             this.searchInferenceId = this.inferenceId;
         }
         this.sourceFields = input.readStringArray();
+        if (input.getTransportVersion().onOrAfter(SEMANTIC_TEXT_CHUNKING_CONFIG_8_19)) {
+            this.chunkingSettings = input.readGenericMap();
+        } else {
+            this.chunkingSettings = null;
+        }
     }
 
     @Override
@@ -71,6 +89,9 @@ public void writeTo(StreamOutput out) throws IOException {
             out.writeString(searchInferenceId);
         }
         out.writeStringArray(sourceFields);
+        if (out.getTransportVersion().onOrAfter(SEMANTIC_TEXT_CHUNKING_CONFIG_8_19)) {
+            out.writeGenericMap(chunkingSettings);
+        }
     }
 
     @Override
@@ -81,16 +102,22 @@ public boolean equals(Object o) {
         return Objects.equals(name, that.name)
             && Objects.equals(inferenceId, that.inferenceId)
             && Objects.equals(searchInferenceId, that.searchInferenceId)
-            && Arrays.equals(sourceFields, that.sourceFields);
+            && Arrays.equals(sourceFields, that.sourceFields)
+            && Objects.equals(chunkingSettings, that.chunkingSettings);
     }
 
     @Override
     public int hashCode() {
-        int result = Objects.hash(name, inferenceId, searchInferenceId);
+        int result = Objects.hash(name, inferenceId, searchInferenceId, chunkingSettings);
         result = 31 * result + Arrays.hashCode(sourceFields);
         return result;
     }
 
+    @Override
+    public String toString() {
+        return Strings.toString(this);
+    }
+
     public String getName() {
         return name;
     }
@@ -107,6 +134,10 @@ public String[] getSourceFields() {
         return sourceFields;
     }
 
+    public Map<String, Object> getChunkingSettings() {
+        return chunkingSettings;
+    }
+
     public static Diff<InferenceFieldMetadata> readDiffFrom(StreamInput in) throws IOException {
         return SimpleDiffable.readDiffFrom(InferenceFieldMetadata::new, in);
     }
@@ -119,6 +150,11 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
             builder.field(SEARCH_INFERENCE_ID_FIELD, searchInferenceId);
         }
         builder.array(SOURCE_FIELDS_FIELD, sourceFields);
+        if (chunkingSettings != null) {
+            builder.startObject(CHUNKING_SETTINGS_FIELD);
+            builder.mapContents(chunkingSettings);
+            builder.endObject();
+        }
         return builder.endObject();
     }
 
@@ -131,6 +167,7 @@ public static InferenceFieldMetadata fromXContent(XContentParser parser) throws
         String currentFieldName = null;
         String inferenceId = null;
         String searchInferenceId = null;
+        Map<String, Object> chunkingSettings = null;
         List<String> inputFields = new ArrayList<>();
         while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
             if (token == XContentParser.Token.FIELD_NAME) {
@@ -151,6 +188,8 @@ public static InferenceFieldMetadata fromXContent(XContentParser parser) throws
                         }
                     }
                 }
+            } else if (CHUNKING_SETTINGS_FIELD.equals(currentFieldName)) {
+                chunkingSettings = parser.map();
             } else {
                 parser.skipChildren();
             }
@@ -159,7 +198,8 @@ public static InferenceFieldMetadata fromXContent(XContentParser parser) throws
             name,
             inferenceId,
             searchInferenceId == null ? inferenceId : searchInferenceId,
-            inputFields.toArray(String[]::new)
+            inputFields.toArray(String[]::new),
+            chunkingSettings
         );
     }
 }

server/src/main/java/org/elasticsearch/inference/ChunkInferenceInput.java

@@ -0,0 +1,25 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.inference;
+
+import org.elasticsearch.core.Nullable;
+
+import java.util.List;
+
+public record ChunkInferenceInput(String input, @Nullable ChunkingSettings chunkingSettings) {
+
+    public ChunkInferenceInput(String input) {
+        this(input, null);
+    }
+
+    public static List<String> inputs(List<ChunkInferenceInput> chunkInferenceInputs) {
+        return chunkInferenceInputs.stream().map(ChunkInferenceInput::input).toList();
+    }
+}

server/src/main/java/org/elasticsearch/inference/ChunkingSettings.java

@@ -12,6 +12,10 @@
 import org.elasticsearch.common.io.stream.VersionedNamedWriteable;
 import org.elasticsearch.xcontent.ToXContentObject;
 
+import java.util.Map;
+
 public interface ChunkingSettings extends ToXContentObject, VersionedNamedWriteable {
     ChunkingStrategy getChunkingStrategy();
+
+    Map<String, Object> asMap();
 }

server/src/main/java/org/elasticsearch/inference/InferenceService.java

@@ -133,18 +133,18 @@ void unifiedCompletionInfer(
     /**
      * Chunk long text.
      *
-     * @param model           The model
-     * @param query           Inference query, mainly for re-ranking
-     * @param input           Inference input
-     * @param taskSettings    Settings in the request to override the model's defaults
-     * @param inputType       For search, ingest etc
-     * @param timeout         The timeout for the request
-     * @param listener        Chunked Inference result listener
+     * @param model            The model
+     * @param query            Inference query, mainly for re-ranking
+     * @param input            Inference input
+     * @param taskSettings     Settings in the request to override the model's defaults
+     * @param inputType        For search, ingest etc
+     * @param timeout          The timeout for the request
+     * @param listener         Chunked Inference result listener
      */
     void chunkedInfer(
         Model model,
         @Nullable String query,
-        List<String> input,
+        List<ChunkInferenceInput> input,
         Map<String, Object> taskSettings,
         InputType inputType,
         TimeValue timeout,

server/src/test/java/org/elasticsearch/cluster/metadata/IndexMetadataTests.java

@@ -694,7 +694,8 @@ private static InferenceFieldMetadata randomInferenceFieldMetadata(String name)
             name,
             randomIdentifier(),
             randomIdentifier(),
-            randomSet(1, 5, ESTestCase::randomIdentifier).toArray(String[]::new)
+            randomSet(1, 5, ESTestCase::randomIdentifier).toArray(String[]::new),
+            InferenceFieldMetadataTests.generateRandomChunkingSettings()
         );
     }
 

server/src/test/java/org/elasticsearch/cluster/metadata/InferenceFieldMetadataTests.java

@@ -15,8 +15,10 @@
 import org.elasticsearch.xcontent.XContentParser;
 
 import java.io.IOException;
+import java.util.Map;
 import java.util.function.Predicate;
 
+import static org.elasticsearch.cluster.metadata.InferenceFieldMetadata.CHUNKING_SETTINGS_FIELD;
 import static org.hamcrest.Matchers.equalTo;
 
 public class InferenceFieldMetadataTests extends AbstractXContentTestCase<InferenceFieldMetadata> {
@@ -37,11 +39,6 @@ protected InferenceFieldMetadata createTestInstance() {
         return createTestItem();
     }
 
-    @Override
-    protected Predicate<String> getRandomFieldsExcludeFilter() {
-        return p -> p.equals(""); // do not add elements at the top-level as any element at this level is parsed as a new inference field
-    }
-
     @Override
     protected InferenceFieldMetadata doParseInstance(XContentParser parser) throws IOException {
         if (parser.nextToken() == XContentParser.Token.START_OBJECT) {
@@ -58,18 +55,57 @@ protected boolean supportsUnknownFields() {
         return true;
     }
 
+    @Override
+    protected Predicate<String> getRandomFieldsExcludeFilter() {
+        // do not add elements at the top-level as any element at this level is parsed as a new inference field,
+        // and do not add additional elements to chunking maps as they will fail parsing with extra data
+        return field -> field.equals("") || field.contains(CHUNKING_SETTINGS_FIELD);
+    }
+
     private static InferenceFieldMetadata createTestItem() {
         String name = randomAlphaOfLengthBetween(3, 10);
         String inferenceId = randomIdentifier();
         String searchInferenceId = randomIdentifier();
         String[] inputFields = generateRandomStringArray(5, 10, false, false);
-        return new InferenceFieldMetadata(name, inferenceId, searchInferenceId, inputFields);
+        Map<String, Object> chunkingSettings = generateRandomChunkingSettings();
+        return new InferenceFieldMetadata(name, inferenceId, searchInferenceId, inputFields, chunkingSettings);
+    }
+
+    public static Map<String, Object> generateRandomChunkingSettings() {
+        if (randomBoolean()) {
+            return null; // Defaults to model chunking settings
+        }
+        return randomBoolean() ? generateRandomWordBoundaryChunkingSettings() : generateRandomSentenceBoundaryChunkingSettings();
+    }
+
+    private static Map<String, Object> generateRandomWordBoundaryChunkingSettings() {
+        return Map.of("strategy", "word_boundary", "max_chunk_size", randomIntBetween(20, 100), "overlap", randomIntBetween(1, 50));
+    }
+
+    private static Map<String, Object> generateRandomSentenceBoundaryChunkingSettings() {
+        return Map.of(
+            "strategy",
+            "sentence_boundary",
+            "max_chunk_size",
+            randomIntBetween(20, 100),
+            "sentence_overlap",
+            randomIntBetween(0, 1)
+        );
     }
 
     public void testNullCtorArgsThrowException() {
-        assertThrows(NullPointerException.class, () -> new InferenceFieldMetadata(null, "inferenceId", "searchInferenceId", new String[0]));
-        assertThrows(NullPointerException.class, () -> new InferenceFieldMetadata("name", null, "searchInferenceId", new String[0]));
-        assertThrows(NullPointerException.class, () -> new InferenceFieldMetadata("name", "inferenceId", null, new String[0]));
-        assertThrows(NullPointerException.class, () -> new InferenceFieldMetadata("name", "inferenceId", "searchInferenceId", null));
+        assertThrows(
+            NullPointerException.class,
+            () -> new InferenceFieldMetadata(null, "inferenceId", "searchInferenceId", new String[0], Map.of())
+        );
+        assertThrows(
+            NullPointerException.class,
+            () -> new InferenceFieldMetadata("name", null, "searchInferenceId", new String[0], Map.of())
+        );
+        assertThrows(NullPointerException.class, () -> new InferenceFieldMetadata("name", "inferenceId", null, new String[0], Map.of()));
+        assertThrows(
+            NullPointerException.class,
+            () -> new InferenceFieldMetadata("name", "inferenceId", "searchInferenceId", null, Map.of())
+        );
     }
 }

server/src/test/java/org/elasticsearch/index/mapper/MappingLookupInferenceFieldMapperTests.java

@@ -11,6 +11,7 @@
 
 import org.apache.lucene.search.Query;
 import org.elasticsearch.cluster.metadata.InferenceFieldMetadata;
+import org.elasticsearch.cluster.metadata.InferenceFieldMetadataTests;
 import org.elasticsearch.index.query.SearchExecutionContext;
 import org.elasticsearch.plugins.MapperPlugin;
 import org.elasticsearch.plugins.Plugin;
@@ -102,7 +103,13 @@ private static class TestInferenceFieldMapper extends FieldMapper implements Inf
 
         @Override
         public InferenceFieldMetadata getMetadata(Set<String> sourcePaths) {
-            return new InferenceFieldMetadata(fullPath(), INFERENCE_ID, SEARCH_INFERENCE_ID, sourcePaths.toArray(new String[0]));
+            return new InferenceFieldMetadata(
+                fullPath(),
+                INFERENCE_ID,
+                SEARCH_INFERENCE_ID,
+                sourcePaths.toArray(new String[0]),
+                InferenceFieldMetadataTests.generateRandomChunkingSettings()
+            );
         }
 
         @Override