Github user lvfangmin commented on a diff in the pull request: https://github.com/apache/zookeeper/pull/684#discussion_r238790553 --- Diff: 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> { --- End diff -- We can extend that, but it's better to be done in a separate thread, feel free to open a new JIRA to follow up on this.
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