Enable engine factory to be pluggable

core/src/main/java/org/elasticsearch/index/IndexModule.java

@@ -39,7 +39,6 @@
 import org.elasticsearch.index.shard.IndexSearcherWrapper;
 import org.elasticsearch.index.shard.IndexingOperationListener;
 import org.elasticsearch.index.shard.SearchOperationListener;
-import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.index.similarity.BM25SimilarityProvider;
 import org.elasticsearch.index.similarity.SimilarityProvider;
 import org.elasticsearch.index.similarity.SimilarityService;
@@ -59,6 +58,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.BiFunction;
@@ -108,8 +108,7 @@ public final class IndexModule {
 
     private final IndexSettings indexSettings;
     private final AnalysisRegistry analysisRegistry;
-    // pkg private so tests can mock
-    final SetOnce<EngineFactory> engineFactory = new SetOnce<>();
+    private final EngineFactory engineFactory;
     private SetOnce<IndexSearcherWrapperFactory> indexSearcherWrapper = new SetOnce<>();
     private final Set<IndexEventListener> indexEventListeners = new HashSet<>();
     private final Map<String, SimilarityProvider.Factory> similarities = new HashMap<>();
@@ -119,9 +118,18 @@ public final class IndexModule {
     private final List<IndexingOperationListener> indexOperationListeners = new ArrayList<>();
     private final AtomicBoolean frozen = new AtomicBoolean(false);
 
-    public IndexModule(IndexSettings indexSettings, AnalysisRegistry analysisRegistry) {
+    /**
+     * Construct the index module for the index with the specified index settings. The index module contains extension points for plugins
+     * via {@link org.elasticsearch.plugins.PluginsService#onIndexModule(IndexModule)}.
+     *
+     * @param indexSettings    the index settings
+     * @param analysisRegistry the analysis registry
+     * @param engineFactory    the engine factory
+     */
+    public IndexModule(final IndexSettings indexSettings, final AnalysisRegistry analysisRegistry, final EngineFactory engineFactory) {
         this.indexSettings = indexSettings;
         this.analysisRegistry = analysisRegistry;
+        this.engineFactory = Objects.requireNonNull(engineFactory);
         this.searchOperationListeners.add(new SearchSlowLog(indexSettings));
         this.indexOperationListeners.add(new IndexingSlowLog(indexSettings));
     }
@@ -162,6 +170,15 @@ public Index getIndex() {
         return indexSettings.getIndex();
     }
 
+    /**
+     * The engine factory provided during construction of this index module.
+     *
+     * @return the engine factory
+     */
+    EngineFactory getEngineFactory() {
+        return engineFactory;
+    }
+
     /**
      * Adds an {@link IndexEventListener} for this index. All listeners added here
      * are maintained for the entire index lifecycle on this node. Once an index is closed or deleted these
@@ -363,7 +380,7 @@ public IndexService newIndexService(
         }
         return new IndexService(indexSettings, environment, xContentRegistry,
                 new SimilarityService(indexSettings, scriptService, similarities),
-                shardStoreDeleter, analysisRegistry, engineFactory.get(), circuitBreakerService, bigArrays, threadPool, scriptService,
+                shardStoreDeleter, analysisRegistry, engineFactory, circuitBreakerService, bigArrays, threadPool, scriptService,
                 client, queryCache, store, eventListener, searcherWrapperFactory, mapperRegistry,
                 indicesFieldDataCache, searchOperationListeners, indexOperationListeners, namedWriteableRegistry);
     }

core/src/main/java/org/elasticsearch/index/IndexService.java

@@ -137,7 +137,7 @@ public IndexService(
             SimilarityService similarityService,
             ShardStoreDeleter shardStoreDeleter,
             AnalysisRegistry registry,
-            @Nullable EngineFactory engineFactory,
+            EngineFactory engineFactory,
             CircuitBreakerService circuitBreakerService,
             BigArrays bigArrays,
             ThreadPool threadPool,
@@ -185,7 +185,7 @@ public IndexService(
         this.warmer = new IndexWarmer(indexSettings.getSettings(), threadPool, indexFieldData,
             bitsetFilterCache.createListener(threadPool));
         this.indexCache = new IndexCache(indexSettings, queryCache, bitsetFilterCache);
-        this.engineFactory = engineFactory;
+        this.engineFactory = Objects.requireNonNull(engineFactory);
         // initialize this last -- otherwise if the wrapper requires any other member to be non-null we fail with an NPE
         this.searcherWrapper = wrapperFactory.newWrapper(this);
         this.searchOperationListeners = Collections.unmodifiableList(searchOperationListeners);
@@ -657,9 +657,9 @@ public interface ShardStoreDeleter {
         void addPendingDelete(ShardId shardId, IndexSettings indexSettings);
     }
 
-    final EngineFactory getEngineFactory() {
+    public final EngineFactory getEngineFactory() {
         return engineFactory;
-    } // pkg private for testing
+    }
 
     final IndexSearcherWrapper getSearcherWrapper() {
         return searcherWrapper;

core/src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -80,7 +80,6 @@
 import org.elasticsearch.index.engine.EngineException;
 import org.elasticsearch.index.engine.EngineFactory;
 import org.elasticsearch.index.engine.InternalEngine;
-import org.elasticsearch.index.engine.InternalEngineFactory;
 import org.elasticsearch.index.engine.RefreshFailedEngineException;
 import org.elasticsearch.index.engine.Segment;
 import org.elasticsearch.index.engine.SegmentsStats;
@@ -195,7 +194,7 @@ public class IndexShard extends AbstractIndexShardComponent implements IndicesCl
     protected volatile IndexShardState state;
     protected volatile long primaryTerm;
     protected final AtomicReference<Engine> currentEngineReference = new AtomicReference<>();
-    protected final EngineFactory engineFactory;
+    final EngineFactory engineFactory;
 
     private final IndexingOperationListener indexingOperationListeners;
     private final Runnable globalCheckpointSyncer;
@@ -265,7 +264,7 @@ public IndexShard(
         this.warmer = warmer;
         this.similarityService = similarityService;
         Objects.requireNonNull(store, "Store must be provided to the index shard");
-        this.engineFactory = engineFactory == null ? new InternalEngineFactory() : engineFactory;
+        this.engineFactory = Objects.requireNonNull(engineFactory);
         this.store = store;
         this.indexSortSupplier = indexSortSupplier;
         this.indexEventListener = indexEventListener;

core/src/main/java/org/elasticsearch/indices/IndicesService.java

@@ -45,6 +45,7 @@
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.breaker.CircuitBreaker;
 import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.component.AbstractLifecycleComponent;
 import org.elasticsearch.common.io.FileSystemUtils;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
@@ -78,6 +79,8 @@
 import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.index.analysis.AnalysisRegistry;
 import org.elasticsearch.index.cache.request.ShardRequestCache;
+import org.elasticsearch.index.engine.EngineFactory;
+import org.elasticsearch.index.engine.InternalEngineFactory;
 import org.elasticsearch.index.fielddata.IndexFieldDataCache;
 import org.elasticsearch.index.flush.FlushStats;
 import org.elasticsearch.index.get.GetStats;
@@ -101,6 +104,7 @@
 import org.elasticsearch.indices.mapper.MapperRegistry;
 import org.elasticsearch.indices.recovery.PeerRecoveryTargetService;
 import org.elasticsearch.indices.recovery.RecoveryState;
+import org.elasticsearch.plugins.EnginePlugin;
 import org.elasticsearch.plugins.PluginsService;
 import org.elasticsearch.repositories.RepositoriesService;
 import org.elasticsearch.script.ScriptService;
@@ -115,10 +119,14 @@
 import java.io.IOException;
 import java.nio.file.Files;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
@@ -169,6 +177,7 @@ public class IndicesService extends AbstractLifecycleComponent
     private final IndicesRequestCache indicesRequestCache;
     private final IndicesQueryCache indicesQueryCache;
     private final MetaStateService metaStateService;
+    private final Collection<EnginePlugin> enginePlugins;
 
     @Override
     protected void doStart() {
@@ -180,7 +189,8 @@ public IndicesService(Settings settings, PluginsService pluginsService, NodeEnvi
                           AnalysisRegistry analysisRegistry, IndexNameExpressionResolver indexNameExpressionResolver,
                           MapperRegistry mapperRegistry, NamedWriteableRegistry namedWriteableRegistry, ThreadPool threadPool,
                           IndexScopedSettings indexScopedSettings, CircuitBreakerService circuitBreakerService, BigArrays bigArrays,
-                          ScriptService scriptService, Client client, MetaStateService metaStateService) {
+                          ScriptService scriptService, Client client, MetaStateService metaStateService,
+                          Collection<EnginePlugin> enginePlugins) {
         super(settings);
         this.threadPool = threadPool;
         this.pluginsService = pluginsService;
@@ -211,6 +221,7 @@ public void onRemoval(ShardId shardId, String fieldName, boolean wasEvicted, lon
         this.cleanInterval = INDICES_CACHE_CLEAN_INTERVAL_SETTING.get(settings);
         this.cacheCleaner = new CacheCleaner(indicesFieldDataCache, indicesRequestCache,  logger, threadPool, this.cleanInterval);
         this.metaStateService = metaStateService;
+        this.enginePlugins = enginePlugins;
     }
 
     @Override
@@ -437,7 +448,7 @@ private synchronized IndexService createIndexService(final String reason,
             idxSettings.getNumberOfReplicas(),
             reason);
 
-        final IndexModule indexModule = new IndexModule(idxSettings, analysisRegistry);
+        final IndexModule indexModule = new IndexModule(idxSettings, analysisRegistry, getEngineFactory(idxSettings));
         for (IndexingOperationListener operationListener : indexingOperationListeners) {
             indexModule.addIndexOperationListener(operationListener);
         }
@@ -461,6 +472,34 @@ private synchronized IndexService createIndexService(final String reason,
         );
     }
 
+    private EngineFactory getEngineFactory(final IndexSettings idxSettings) {
+        final List<Tuple<EnginePlugin, Optional<EngineFactory>>> engineFactories =
+                enginePlugins
+                        .stream()
+                        .map(p -> Tuple.tuple(p, p.getEngineFactory(idxSettings)))
+                        .filter(t -> Objects.requireNonNull(t.v2()).isPresent())
+                        .collect(Collectors.toList());
+        if (engineFactories.isEmpty()) {
+            return new InternalEngineFactory();
+        } else if (engineFactories.size() == 1) {
+            assert engineFactories.get(0).v2().isPresent();
+            return engineFactories.get(0).v2().get();
+        } else {
+            final String message = String.format(
+                    Locale.ROOT,
+                    "multiple plugins provided engine factories for %s: %s",
+                    idxSettings.getIndex(),
+                    engineFactories
+                            .stream()
+                            .map(t -> {
+                                assert t.v2().isPresent();
+                                return "[" + t.v1().getClass().getName() + "/" + t.v2().get().getClass().getName() + "]";
+                            })
+                            .collect(Collectors.joining(",")));
+            throw new IllegalStateException(message);
+        }
+    }
+
     /**
      * creates a new mapper service for the given index, in order to do administrative work like mapping updates.
      * This *should not* be used for document parsing. Doing so will result in an exception.
@@ -469,7 +508,7 @@ private synchronized IndexService createIndexService(final String reason,
      */
     public synchronized MapperService createIndexMapperService(IndexMetaData indexMetaData) throws IOException {
         final IndexSettings idxSettings = new IndexSettings(indexMetaData, this.settings, indexScopeSetting);
-        final IndexModule indexModule = new IndexModule(idxSettings, analysisRegistry);
+        final IndexModule indexModule = new IndexModule(idxSettings, analysisRegistry, getEngineFactory(idxSettings));
         pluginsService.onIndexModule(indexModule);
         return indexModule.newIndexMapperService(xContentRegistry, mapperRegistry, scriptService);
     }

core/src/main/java/org/elasticsearch/node/Node.java

@@ -100,7 +100,6 @@
 import org.elasticsearch.indices.breaker.HierarchyCircuitBreakerService;
 import org.elasticsearch.indices.breaker.NoneCircuitBreakerService;
 import org.elasticsearch.indices.cluster.IndicesClusterStateService;
-import org.elasticsearch.indices.mapper.MapperRegistry;
 import org.elasticsearch.indices.recovery.PeerRecoverySourceService;
 import org.elasticsearch.indices.recovery.PeerRecoveryTargetService;
 import org.elasticsearch.indices.recovery.RecoverySettings;
@@ -112,6 +111,7 @@
 import org.elasticsearch.plugins.AnalysisPlugin;
 import org.elasticsearch.plugins.ClusterPlugin;
 import org.elasticsearch.plugins.DiscoveryPlugin;
+import org.elasticsearch.plugins.EnginePlugin;
 import org.elasticsearch.plugins.IngestPlugin;
 import org.elasticsearch.plugins.MapperPlugin;
 import org.elasticsearch.plugins.MetaDataUpgrader;
@@ -385,11 +385,15 @@ protected Node(final Environment environment, Collection<Class<? extends Plugin>
                 .flatMap(Function.identity()).collect(toList()));
             modules.add(new RepositoriesModule(this.environment, pluginsService.filterPlugins(RepositoryPlugin.class), xContentRegistry));
             final MetaStateService metaStateService = new MetaStateService(settings, nodeEnvironment, xContentRegistry);
-            final IndicesService indicesService = new IndicesService(settings, pluginsService, nodeEnvironment, xContentRegistry,
-                    analysisModule.getAnalysisRegistry(),
-                clusterModule.getIndexNameExpressionResolver(), indicesModule.getMapperRegistry(), namedWriteableRegistry,
-                threadPool, settingsModule.getIndexScopedSettings(), circuitBreakerService, bigArrays, scriptModule.getScriptService(),
-                client, metaStateService);
+
+            // collect engine factory providers per plugin
+            final Collection<EnginePlugin> enginePlugins = pluginsService.filterPlugins(EnginePlugin.class);
+
+            final IndicesService indicesService =
+                    new IndicesService(settings, pluginsService, nodeEnvironment, xContentRegistry, analysisModule.getAnalysisRegistry(),
+                            clusterModule.getIndexNameExpressionResolver(), indicesModule.getMapperRegistry(), namedWriteableRegistry,
+                            threadPool, settingsModule.getIndexScopedSettings(), circuitBreakerService, bigArrays,
+                            scriptModule.getScriptService(), client, metaStateService, enginePlugins);
 
             Collection<Object> pluginComponents = pluginsService.filterPlugins(Plugin.class).stream()
                 .flatMap(p -> p.createComponents(client, clusterService, threadPool, resourceWatcherService,

core/src/main/java/org/elasticsearch/plugins/EnginePlugin.java

@@ -0,0 +1,42 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.plugins;
+
+import org.elasticsearch.index.IndexSettings;
+import org.elasticsearch.index.engine.EngineFactory;
+
+import java.util.Optional;
+
+/**
+ * A plugin that provides alternative engine implementations.
+ */
+public interface EnginePlugin {
+
+    /**
+     * When an index is created this method is invoked for each engine plugin. Engine plugins can inspect the index settings to determine
+     * whether or not to provide an engine factory for the given index. A plugin that is not overriding the default engine should return
+     * {@link Optional#empty()}. If multiple plugins return an engine factory for a given index the index will not be created and an
+     * {@link IllegalStateException} will be thrown during index creation.
+     *
+     * @return an optional engine factory
+     */
+    Optional<EngineFactory> getEngineFactory(IndexSettings indexSettings);
+
+}