Remove ElasticsearchQueryCachingPolicy (#27190)

We have an hidden setting called `index.queries.cache.term_queries` that disables caching of term queries in the query cache.
Though term queries are not cached in the Lucene UsageTrackingQueryCachingPolicy since version 6.5.
This makes the es policy useless but also makes it impossible to re-enable caching for term queries.
This change appeared in Lucene 6.5 so this setting is no-op since version 5.4 of Elasticsearch
The change in this PR removes the setting and the custom policy.

core/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java

@@ -145,7 +145,6 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
         IndexModule.INDEX_STORE_PRE_LOAD_SETTING,
         IndexModule.INDEX_QUERY_CACHE_ENABLED_SETTING,
         IndexModule.INDEX_QUERY_CACHE_EVERYTHING_SETTING,
-        IndexModule.INDEX_QUERY_CACHE_TERM_QUERIES_SETTING,
         FsDirectoryService.INDEX_LOCK_FACTOR_SETTING,
         EngineConfig.INDEX_CODEC_SETTING,
         EngineConfig.INDEX_OPTIMIZE_AUTO_GENERATED_IDS,

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

@@ -101,11 +101,6 @@ public final class IndexModule {
     public static final Setting<Boolean> INDEX_QUERY_CACHE_EVERYTHING_SETTING =
         Setting.boolSetting("index.queries.cache.everything", false, Property.IndexScope);
 
-    // This setting is an escape hatch in case not caching term queries would slow some users down
-    // Do not document.
-    public static final Setting<Boolean> INDEX_QUERY_CACHE_TERM_QUERIES_SETTING =
-        Setting.boolSetting("index.queries.cache.term_queries", false, Property.IndexScope);
-
     private final IndexSettings indexSettings;
     private final AnalysisRegistry analysisRegistry;
     // pkg private so tests can mock

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

@@ -1,56 +0,0 @@
-/*
- * 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.shard;
-
-import org.apache.lucene.search.Query;
-import org.apache.lucene.search.QueryCachingPolicy;
-import org.apache.lucene.search.TermQuery;
-
-import java.io.IOException;
-
-/**
- * A {@link QueryCachingPolicy} that does not cache {@link TermQuery}s.
- */
-final class ElasticsearchQueryCachingPolicy implements QueryCachingPolicy {
-
-    private final QueryCachingPolicy in;
-
-    ElasticsearchQueryCachingPolicy(QueryCachingPolicy in) {
-        this.in = in;
-    }
-
-    @Override
-    public void onUse(Query query) {
-        if (query.getClass() != TermQuery.class) {
-            // Do not waste space in the history for term queries. The assumption
-            // is that these queries are very fast so not worth caching
-            in.onUse(query);
-        }
-    }
-
-    @Override
-    public boolean shouldCache(Query query) throws IOException {
-        if (query.getClass() == TermQuery.class) {
-            return false;
-        }
-        return in.shouldCache(query);
-    }
-
-}

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

@@ -291,11 +291,7 @@ public class IndexShard extends AbstractIndexShardComponent implements IndicesCl
         if (IndexModule.INDEX_QUERY_CACHE_EVERYTHING_SETTING.get(settings)) {
             cachingPolicy = QueryCachingPolicy.ALWAYS_CACHE;
         } else {
-            QueryCachingPolicy cachingPolicy = new UsageTrackingQueryCachingPolicy();
+            cachingPolicy = new UsageTrackingQueryCachingPolicy();
-            if (IndexModule.INDEX_QUERY_CACHE_TERM_QUERIES_SETTING.get(settings) == false) {
-                cachingPolicy = new ElasticsearchQueryCachingPolicy(cachingPolicy);
-            }
-            this.cachingPolicy = cachingPolicy;
         }
         indexShardOperationPermits = new IndexShardOperationPermits(shardId, logger, threadPool);
         searcherWrapper = indexSearcherWrapper;

core/src/test/java/org/elasticsearch/index/shard/ElasticsearchQueryCachingPolicyTests.java

@@ -1,61 +0,0 @@
-/*
- * 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.shard;
-
-import org.apache.lucene.index.Term;
-import org.apache.lucene.search.PhraseQuery;
-import org.apache.lucene.search.Query;
-import org.apache.lucene.search.QueryCachingPolicy;
-import org.apache.lucene.search.TermQuery;
-import org.elasticsearch.test.ESTestCase;
-
-import java.io.IOException;
-
-public class ElasticsearchQueryCachingPolicyTests extends ESTestCase {
-
-    public void testDoesNotCacheTermQueries() throws IOException {
-        QueryCachingPolicy policy = QueryCachingPolicy.ALWAYS_CACHE;
-        assertTrue(policy.shouldCache(new TermQuery(new Term("foo", "bar"))));
-        assertTrue(policy.shouldCache(new PhraseQuery("foo", "bar", "baz")));
-        policy = new ElasticsearchQueryCachingPolicy(policy);
-        assertFalse(policy.shouldCache(new TermQuery(new Term("foo", "bar"))));
-        assertTrue(policy.shouldCache(new PhraseQuery("foo", "bar", "baz")));
-    }
-
-    public void testDoesNotPutTermQueriesIntoTheHistory() {
-        boolean[] used = new boolean[1];
-        QueryCachingPolicy policy = new QueryCachingPolicy() {
-            @Override
-            public boolean shouldCache(Query query) throws IOException {
-                throw new UnsupportedOperationException();
-            }
-            @Override
-            public void onUse(Query query) {
-                used[0] = true;
-            }
-        };
-        policy = new ElasticsearchQueryCachingPolicy(policy);
-        policy.onUse(new TermQuery(new Term("foo", "bar")));
-        assertFalse(used[0]);
-        policy.onUse(new PhraseQuery("foo", "bar", "baz"));
-        assertTrue(used[0]);
-    }
-
-}

test/framework/src/main/java/org/elasticsearch/test/ESIntegTestCase.java

@@ -429,9 +429,6 @@ public abstract class ESIntegTestCase extends ESTestCase {
             if (randomBoolean()) {
                 randomSettingsBuilder.put(IndexModule.INDEX_QUERY_CACHE_EVERYTHING_SETTING.getKey(), randomBoolean());
             }
-            if (randomBoolean()) {
-                randomSettingsBuilder.put(IndexModule.INDEX_QUERY_CACHE_TERM_QUERIES_SETTING.getKey(), randomBoolean());
-            }
             PutIndexTemplateRequestBuilder putTemplate = client().admin().indices()
                 .preparePutTemplate("random_index_template")
                 .setPatterns(Collections.singletonList("*"))