Allow plugins to register custom `QueryCache` implementations.

core/src/main/java/org/elasticsearch/index/cache/IndexCacheModule.java

@@ -20,8 +20,8 @@
 package org.elasticsearch.index.cache;
 
 import org.elasticsearch.common.inject.AbstractModule;
-import org.elasticsearch.common.inject.Scopes;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.util.ExtensionPoint;
 import org.elasticsearch.index.cache.bitset.BitsetFilterCache;
 import org.elasticsearch.index.cache.query.QueryCache;
 import org.elasticsearch.index.cache.query.index.IndexQueryCache;
@@ -35,24 +35,24 @@ public class IndexCacheModule extends AbstractModule {
     // for test purposes only
     public static final String QUERY_CACHE_EVERYTHING = "index.queries.cache.everything";
 
-    private final Settings settings;
+    private final Settings indexSettings;
+    private final ExtensionPoint.TypeExtensionPoint<QueryCache> queryCaches;
 
     public IndexCacheModule(Settings settings) {
-        this.settings = settings;
+        this.indexSettings = settings;
+        this.queryCaches = new ExtensionPoint.TypeExtensionPoint<>("query_cache", QueryCache.class);
+
+        registerQueryCache(INDEX_QUERY_CACHE, IndexQueryCache.class);
+        registerQueryCache(NONE_QUERY_CACHE, NoneQueryCache.class);
+    }
+
+    public void registerQueryCache(String name, Class<? extends QueryCache> clazz) {
+        queryCaches.registerExtension(name, clazz);
     }
 
     @Override
     protected void configure() {
-        String queryCacheType = settings.get(QUERY_CACHE_TYPE, INDEX_QUERY_CACHE);
-        Class<? extends QueryCache> queryCacheImpl;
-        if (queryCacheType.equals(INDEX_QUERY_CACHE)) {
-            queryCacheImpl = IndexQueryCache.class;
-        } else if (queryCacheType.equals(NONE_QUERY_CACHE)) {
-            queryCacheImpl = NoneQueryCache.class;
-        } else {
-            throw new IllegalArgumentException("Unknown QueryCache type [" + queryCacheType + "]");
-        }
-        bind(QueryCache.class).to(queryCacheImpl).in(Scopes.SINGLETON);
+        queryCaches.bindType(binder(), indexSettings, QUERY_CACHE_TYPE, INDEX_QUERY_CACHE);
         bind(BitsetFilterCache.class).asEagerSingleton();
         bind(IndexCache.class).asEagerSingleton();
     }

core/src/test/java/org/elasticsearch/index/cache/IndexCacheModuleTests.java

@@ -0,0 +1,89 @@
+/*
+ * 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.index.cache;
+
+import org.apache.lucene.search.QueryCachingPolicy;
+import org.apache.lucene.search.Weight;
+import org.elasticsearch.common.inject.ModuleTestCase;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.index.Index;
+import org.elasticsearch.index.cache.query.QueryCache;
+import org.elasticsearch.index.cache.query.index.IndexQueryCache;
+import org.elasticsearch.index.cache.query.none.NoneQueryCache;
+
+import java.io.IOException;
+
+public class IndexCacheModuleTests extends ModuleTestCase {
+
+    public void testCannotRegisterProvidedImplementations() {
+        IndexCacheModule module = new IndexCacheModule(Settings.EMPTY);
+        try {
+            module.registerQueryCache("index", IndexQueryCache.class);
+        } catch (IllegalArgumentException e) {
+            assertEquals(e.getMessage(), "Can't register the same [query_cache] more than once for [index]");
+        }
+
+        try {
+            module.registerQueryCache("none", NoneQueryCache.class);
+        } catch (IllegalArgumentException e) {
+            assertEquals(e.getMessage(), "Can't register the same [query_cache] more than once for [none]");
+        }
+    }
+
+    public void testRegisterCustomQueryCache() {
+        IndexCacheModule module = new IndexCacheModule(
+                Settings.builder().put(IndexCacheModule.QUERY_CACHE_TYPE, "custom").build()
+        );
+        module.registerQueryCache("custom", CustomQueryCache.class);
+        try {
+            module.registerQueryCache("custom", CustomQueryCache.class);
+        } catch (IllegalArgumentException e) {
+            assertEquals(e.getMessage(), "Can't register the same [query_cache] more than once for [custom]");
+        }
+        assertBinding(module, QueryCache.class, CustomQueryCache.class);
+    }
+
+    public void testDefaultQueryCacheImplIsSelected() {
+        IndexCacheModule module = new IndexCacheModule(Settings.EMPTY);
+        assertBinding(module, QueryCache.class, IndexQueryCache.class);
+    }
+
+    class CustomQueryCache implements QueryCache {
+
+        @Override
+        public void clear(String reason) {
+        }
+
+        @Override
+        public void close() throws IOException {
+        }
+
+        @Override
+        public Index index() {
+            return new Index("test");
+        }
+
+        @Override
+        public Weight doCache(Weight weight, QueryCachingPolicy policy) {
+            return weight;
+        }
+    }
+
+}