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Subject [GitHub] enixon commented on a change in pull request #684: ZOOKEEPER-3180: Add response cache to improve the throughput of read …
Date Fri, 11 Jan 2019 22:42:24 GMT
enixon commented on a change in pull request #684: ZOOKEEPER-3180: Add response cache to improve
the throughput of read …
URL: https://github.com/apache/zookeeper/pull/684#discussion_r247275626
 
 

 ##########
 File path: zookeeper-server/src/main/java/org/apache/zookeeper/server/ResponseCache.java
 ##########
 @@ -0,0 +1,84 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.zookeeper.server;
+
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.apache.jute.Record;
+import org.apache.zookeeper.data.Stat;
+
+@SuppressWarnings("serial")
+public class ResponseCache {
+    private static final int DEFAULT_RESPONSE_CACHE_SIZE = 400;
+
+    private static class Entry {
+        public Stat stat;
+        public byte[] data;
+    }
+
+    private Map<String, Entry> cache = Collections.synchronizedMap(
+        new LRUCache<String, Entry>(getResponseCacheSize()));
+
+    public ResponseCache() {
+    }
+
+    public void put(String path, byte[] data, Stat stat) {
+        Entry entry = new Entry();
+        entry.data = data;
+        entry.stat = stat;
+        cache.put(path, entry);
+    }
+
+    public byte[] get(String key, Stat stat) {
+        Entry entry = cache.get(key);
+        if (entry == null) {
+            return null;
+        }
+        if (!stat.equals(entry.stat)) {
+            // The node has been modified, invalidate cache.
+            cache.remove(key);
+            return null;
+        } else {
+            return entry.data;
+        }
+    }
+
+    private static int getResponseCacheSize() {
+        String value = System.getProperty("zookeeper.maxResponseCacheSize");
+        return value == null ? DEFAULT_RESPONSE_CACHE_SIZE : Integer.parseInt(value);
+    }
+
+    public static boolean isEnabled() {
+        return getResponseCacheSize() != 0;
+    }
+
+    private static class LRUCache<K, V> extends LinkedHashMap<K, V> {
+        private int cacheSize;
+
+        public LRUCache(int cacheSize) {
 
 Review comment:
   We haven't tested or considered the alternate eviction policies you outline and that LinkedHashMap
allows. I see three reasonable paths here, @hanm  @anmolnar  @lvfangmin .
   
   - Merge this pr as it is (perhaps rename LRUCache to just Cache) and open a new JIRA to
explore future paths.
   - I add another property that lets one toggle between insertion order and access order
with the current implementation as the default.
   - Drop LinkedHashMap entirely and go with something like a guava Cache.
   
   My preference is to merge something as close to the current implementation as possible
so that others can start to enjoy the benefits of the ResponseCache and open a JIRA so the
task of extending the cache functionality goes to someone enthusiastic about tackling new
feature work. Thoughts?

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