Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/590#discussion_r219912709
--- Diff:
src/java/main/org/apache/zookeeper/server/watch/WatchManagerOptimized.java ---
@@ -0,0 +1,355 @@
+/**
+ * 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.watch;
+
+import java.io.PrintWriter;
+import java.util.HashMap;
+import java.util.BitSet;
+import java.util.HashSet;
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Random;
+import java.util.Set;
+import java.util.Iterator;
+import java.lang.Iterable;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+import org.apache.zookeeper.WatchedEvent;
+import org.apache.zookeeper.Watcher;
+import org.apache.zookeeper.Watcher.Event.EventType;
+import org.apache.zookeeper.Watcher.Event.KeeperState;
+import org.apache.zookeeper.server.ServerCnxn;
+import org.apache.zookeeper.server.util.BitMap;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Optimized in memory and time complexity, compared to WatchManager, both
the
+ * memory consumption and time complexity improved a lot, but it cannot
+ * efficiently remove the watcher when the session or socket is closed, for
+ * majority usecase this is not a problem.
--- End diff --
nit: use case
---
