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From hanm <...@git.apache.org>
Subject [GitHub] zookeeper pull request #590: [ZOOKEEPER-1177] Add the memory optimized watch...
Date Sat, 22 Sep 2018 04:38:36 GMT
Github user hanm commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/590#discussion_r219659984
  
    --- Diff: src/java/main/org/apache/zookeeper/server/watch/BitHashSet.java ---
    @@ -0,0 +1,156 @@
    +/**
    + * 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.util.BitSet;
    +import java.util.Set;
    +import java.util.HashSet;
    +import java.util.Iterator;
    +import java.lang.Iterable;
    +
    +import org.apache.zookeeper.server.util.BitMap;
    +
    +/**
    + * Using BitSet to store all the elements, and use HashSet to cache limited
    + * number of elements to find a balance between memory and time complexity.
    + *
    + * Without HashSet, we need to to use O(N) time to get the elements, N is
    + * the bit numbers in elementBits. But we need to keep the size small to make
    + * sure it doesn't cost too much in memory, there is a tradeoff between
    + * memory and time complexity.
    + *
    + * Previously, was deciding to dynamically switch between SparseBitSet and
    + * HashSet based on the memory consumption, but it will take time to copy
    + * data over and may have some herd effect of keep copying data from one
    + * data structure to anther. The current solution can do a very good job
    + * given most of the paths have limited number of elements.
    + */
    +public class BitHashSet implements Iterable<Integer> {
    +
    +    static final long serialVersionUID = 6382565447128283568L;
    --- End diff --
    
    why do we need this? `BitHashSet` is not implementing `Serializable` here...


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