ConsistentHash 实现_consistenthash.get()-优快云博客

本文介绍了一致性哈希算法的实现，通过创建环形哈希空间并利用虚拟节点提高负载均衡性能。具体包括添加和移除节点的方法，以及如何根据键找到对应的节点。

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1、创建环形hash空间，并依据复制品的个数在hash空间创建实际节点对应的虚拟节点

2、依据key在环形hash空间中，找到其对应的实际节点

import java.util.SortedMap;
import java.util.TreeMap;

public class ConsistentHash {
    /**
    * hash函数
    */
    private final CRC32 hashFunction = new CRC32();
    /**
    * 虚拟节点是实际节点在 hash 空间的复制品
    */
    private final int numberOfReplicas;
    /**
    * 环形hash空间
    */
    private final SortedMap<Long, String> circle = new TreeMap<Long, String>();

    public ConsistentHash(int numberOfReplicas, String[] servers) {
        this.numberOfReplicas = numberOfReplicas;
        for (int i = 0; i < servers.length; i++) {
            add(servers[i]);
        }
        System.out.println("::::"+circle);
    }
    /**
    * 在hash空间添加虚拟节点对应的实际节点
    * @param server
    */
    public void add(String server) {
        for (int i = 0; i < numberOfReplicas; i++) {
            circle.put(hashFunction.hash(server.toString() + i), server);
        }
    }
    /**
    * 删除hash空间中虚拟节点对应的实际节点
    * @param server
    */
    public void remove(String server) {
        for (int i = 0; i < numberOfReplicas; i++) {
            circle.remove(hashFunction.hash(server.toString() + i));
        }
    }
    /**
    * 依据key查询对应的实际节点
    * @param key
    * @return
    */
    public String get(Object key) {
        if (circle.isEmpty()) {
            return null;
        }
        Long hash = hashFunction.hash(key.toString());
//        System.out.println(key+"-->"+hash);
        if (!circle.containsKey(hash)) {
            SortedMap<Long, String> tailMap = circle.tailMap(hash);
            hash = tailMap.isEmpty() ? circle.firstKey() : tailMap.firstKey();
        }
        return circle.get(hash);
    }
}

memcache 实现

static String[] servers = { "172.16.24.203:11211","192.168.1.173:11211" };
    public static void main(String[] args) {
        // memcached should be running on port 11211 but NOT on 11212
        //cmd > memcached.exe -p 2000
        BasicConfigurator.configure();
//        Integer[] weights = { 3,2 };
        SockIOPool pool = SockIOPool.getInstance("test");
        pool.setServers( servers );
        pool.setFailover( true );
        pool.setInitConn( 10 );
        pool.setMinConn( 5 );
        pool.setMaxConn( 250 );
        //pool.setMaintSleep( 30 );
        pool.setNagle( false );
        pool.setSocketTO( 3000 );
        pool.setAliveCheck( true );
//        pool.setWeights(weights);
        pool.initialize();

        MemCachedClient mcc = new MemCachedClient("test");
        // turn off most memcached client logging:
        //Logger.getLogger( MemCachedClient.class.getName() ).setLevel( com.schooner.MemCached.Logger. );
//        System.out.println("flushAll returen : "+mcc.flushAll(servers));

        ConsistentHash consistentHash = new ConsistentHash(2,servers);

//        consistentHash.remove(servers[0]);

        for (int i = 0; i < 10; i++) {
            String key = "object" + i;
            String obj1Cache = consistentHash.get(key);
            System.out.println(key + " node-->" + obj1Cache);
            String value1 = key + " Hello!";
            boolean success = mcc.set(key, value1, obj1Cache.hashCode());
            System.out.println(String.format("set( %s ): %s", key, success));
            String result = (String) mcc.get(key, obj1Cache.hashCode());
            System.out.println(String.format("get( %s ): %s", key, result));
        }