Extensible Completion Postings Formats (elastic#111494)

Allows the Completion Postings Format to be extensible by providing an implementation of the CompletionsPostingsFormatExtension SPIs.

Author: JVerwolf

docs/changelog/111494.yaml

@@ -0,0 +1,5 @@
+pr: 111494
+summary: Extensible Completion Postings Formats
+area: "Suggesters"
+type: enhancement
+issues: []

server/src/main/java/module-info.java

@@ -7,6 +7,7 @@
  * License v3.0 only", or the "Server Side Public License, v 1".
  */
 
+import org.elasticsearch.internal.CompletionsPostingsFormatExtension;
 import org.elasticsearch.plugins.internal.RestExtension;
 
 /** The Elasticsearch Server Module. */
@@ -288,7 +289,8 @@
         to
             org.elasticsearch.serverless.version,
             org.elasticsearch.serverless.buildinfo,
-            org.elasticsearch.serverless.constants;
+            org.elasticsearch.serverless.constants,
+            org.elasticsearch.serverless.codec;
     exports org.elasticsearch.lucene.analysis.miscellaneous;
     exports org.elasticsearch.lucene.grouping;
     exports org.elasticsearch.lucene.queries;
@@ -395,6 +397,7 @@
             org.elasticsearch.stateless,
             org.elasticsearch.settings.secure,
             org.elasticsearch.serverless.constants,
+            org.elasticsearch.serverless.codec,
             org.elasticsearch.serverless.apifiltering,
             org.elasticsearch.internal.security;
 
@@ -414,6 +417,7 @@
     uses org.elasticsearch.node.internal.TerminationHandlerProvider;
     uses org.elasticsearch.internal.VersionExtension;
     uses org.elasticsearch.internal.BuildExtension;
+    uses CompletionsPostingsFormatExtension;
     uses org.elasticsearch.features.FeatureSpecification;
     uses org.elasticsearch.plugins.internal.LoggingDataProvider;
 

server/src/main/java/org/elasticsearch/index/codec/PerFieldFormatSupplier.java

@@ -20,10 +20,15 @@
 import org.elasticsearch.index.codec.bloomfilter.ES87BloomFilterPostingsFormat;
 import org.elasticsearch.index.codec.postings.ES812PostingsFormat;
 import org.elasticsearch.index.codec.tsdb.ES87TSDBDocValuesFormat;
+import org.elasticsearch.index.mapper.CompletionFieldMapper;
 import org.elasticsearch.index.mapper.IdFieldMapper;
 import org.elasticsearch.index.mapper.Mapper;
 import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper;
+import org.elasticsearch.internal.CompletionsPostingsFormatExtension;
+import org.elasticsearch.plugins.ExtensionLoader;
+
+import java.util.ServiceLoader;
 
 /**
  * Class that encapsulates the logic of figuring out the most appropriate file format for a given field, across postings, doc values and
@@ -53,15 +58,28 @@ public PostingsFormat getPostingsFormatForField(String field) {
 
     private PostingsFormat internalGetPostingsFormatForField(String field) {
         if (mapperService != null) {
-            final PostingsFormat format = mapperService.mappingLookup().getPostingsFormat(field);
-            if (format != null) {
-                return format;
+            Mapper mapper = mapperService.mappingLookup().getMapper(field);
+            if (mapper instanceof CompletionFieldMapper) {
+                return PostingsFormatHolder.POSTINGS_FORMAT;
             }
         }
         // return our own posting format using PFOR
         return es812PostingsFormat;
     }
 
+    private static class PostingsFormatHolder {
+        private static final PostingsFormat POSTINGS_FORMAT = getPostingsFormat();
+
+        private static PostingsFormat getPostingsFormat() {
+            String defaultName = "Completion912"; // Caution: changing this name will result in exceptions if a field is created during a
+            // rolling upgrade and the new codec (specified by the name) is not available on all nodes in the cluster.
+            String codecName = ExtensionLoader.loadSingleton(ServiceLoader.load(CompletionsPostingsFormatExtension.class))
+                .map(CompletionsPostingsFormatExtension::getFormatName)
+                .orElse(defaultName);
+            return PostingsFormat.forName(codecName);
+        }
+    }
+
     boolean useBloomFilter(String field) {
         if (mapperService == null) {
             return false;

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

@@ -8,7 +8,6 @@
  */
 package org.elasticsearch.index.mapper;
 
-import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.document.FieldType;
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.Term;
@@ -344,10 +343,6 @@ public CompletionFieldType fieldType() {
         return (CompletionFieldType) super.fieldType();
     }
 
-    static PostingsFormat postingsFormat() {
-        return PostingsFormat.forName("Completion912");
-    }
-
     @Override
     public boolean parsesArrayValue() {
         return true;

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

@@ -9,7 +9,6 @@
 
 package org.elasticsearch.index.mapper;
 
-import org.apache.lucene.codecs.PostingsFormat;
 import org.elasticsearch.cluster.metadata.DataStream;
 import org.elasticsearch.cluster.metadata.InferenceFieldMetadata;
 import org.elasticsearch.index.IndexSettings;
@@ -21,7 +20,6 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -58,7 +56,6 @@ private CacheKey() {}
     private final Map<String, NamedAnalyzer> indexAnalyzersMap;
     private final List<FieldMapper> indexTimeScriptMappers;
     private final Mapping mapping;
-    private final Set<String> completionFields;
     private final int totalFieldsCount;
 
     /**
@@ -161,7 +158,6 @@ private MappingLookup(
         this.nestedLookup = NestedLookup.build(nestedMappers);
 
         final Map<String, NamedAnalyzer> indexAnalyzersMap = new HashMap<>();
-        final Set<String> completionFields = new HashSet<>();
         final List<FieldMapper> indexTimeScriptMappers = new ArrayList<>();
         for (FieldMapper mapper : mappers) {
             if (objects.containsKey(mapper.fullPath())) {
@@ -174,9 +170,6 @@ private MappingLookup(
             if (mapper.hasScript()) {
                 indexTimeScriptMappers.add(mapper);
             }
-            if (mapper instanceof CompletionFieldMapper) {
-                completionFields.add(mapper.fullPath());
-            }
         }
 
         for (FieldAliasMapper aliasMapper : aliasMappers) {
@@ -211,7 +204,6 @@ private MappingLookup(
         this.objectMappers = Map.copyOf(objects);
         this.runtimeFieldMappersCount = runtimeFields.size();
         this.indexAnalyzersMap = Map.copyOf(indexAnalyzersMap);
-        this.completionFields = Set.copyOf(completionFields);
         this.indexTimeScriptMappers = List.copyOf(indexTimeScriptMappers);
 
         runtimeFields.stream().flatMap(RuntimeField::asMappedFieldTypes).map(MappedFieldType::name).forEach(this::validateDoesNotShadow);
@@ -285,15 +277,6 @@ public Iterable<Mapper> fieldMappers() {
         return fieldMappers.values();
     }
 
-    /**
-     * Gets the postings format for a particular field
-     * @param field the field to retrieve a postings format for
-     * @return the postings format for the field, or {@code null} if the default format should be used
-     */
-    public PostingsFormat getPostingsFormat(String field) {
-        return completionFields.contains(field) ? CompletionFieldMapper.postingsFormat() : null;
-    }
-
     void checkLimits(IndexSettings settings) {
         checkFieldLimit(settings.getMappingTotalFieldsLimit());
         checkObjectDepthLimit(settings.getMappingDepthLimit());

server/src/main/java/org/elasticsearch/internal/CompletionsPostingsFormatExtension.java

@@ -0,0 +1,28 @@
+/*
+ * 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.internal;
+
+import org.apache.lucene.search.suggest.document.CompletionPostingsFormat;
+
+/**
+ * Allows plugging-in the Completions Postings Format.
+ */
+public interface CompletionsPostingsFormatExtension {
+
+    /**
+     * Returns the name of the  {@link CompletionPostingsFormat} that Elasticsearch should use. Should return null if the extension
+     * is not enabled.
+     * <p>
+     * Note that the name must match a codec that is available on all nodes in the cluster, otherwise IndexCorruptionExceptions will occur.
+     * A feature can be used to protect against this scenario, or alternatively, the codec code can be rolled out prior to its usage by this
+     * extension.
+     */
+    String getFormatName();
+}