Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/684#discussion_r229934517
--- 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 --
nice.
---
