一致性hash算法Consistent Hashing

一致性hash算法Consistent Hashing

对于原有hash算法hash%n



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1.话不多说直接上代码,原理或详解自行百度即可

import cn.pheker.utils.UtilElapsedTime;
import cn.pheker.utils.UtilLogger;
import cn.pheker.utils.UtilMD5;

import java.util.*;

/**
 * <pre>
 * author    cn.pheker
 * date      2018/3/19 10:20
 * email     1176479642@qq.com
 * desc      一致性哈希算法
 *
 * </pre>
 */
public class ConsistentHashing {

    private static final long MIN_NODE_NUMBER = 0;
    private static final int MAX_NODE_NUMBER = Integer.MAX_VALUE;
    private static int VIRTUAL_NODE_NUMBER;

    //真实节点
    private List<Node> realNodes = new LinkedList<Node>();
    //虚拟节点,hash环
    private SortedMap<Integer, VNode> circle = new TreeMap<Integer, VNode>();

    private ConsistentHashing(int vnNumber) {
        VIRTUAL_NODE_NUMBER = vnNumber;
    }

    public static ConsistentHashing build(int vnNumber) {
        return new ConsistentHashing(vnNumber);
    }

    public ConsistentHashing addNode(Map<String,String> ipPorts) {
        Set<String> ips = ipPorts.keySet();
        Iterator<String> ipite = ips.iterator();
        while(ipite.hasNext()){
            String ip = ipite.next();
            addNode(ip, ipPorts.get(ip));
        }
        return this;
    }

    public ConsistentHashing addNode(String ip, int port) {
        addNode(ip, String.valueOf(port));
        return this;
    }

    public ConsistentHashing addNode(String ip, String port) {
        Node node = new Node(ip, port);
        if (!realNodes.contains(node)) {
            realNodes.add(node);
            UtilLogger.println("[Node]:"+node.toString()+" Hash:"+node.hashFNV1_32());
            //生成VIRTUAL_NODE_NUMBER个虚拟节点
            for (int i = 0; i < VIRTUAL_NODE_NUMBER; i++) {
                VNode vNode = node.createVNode(i);
                circle.put(vNode.hashFNV1_32(), vNode);
                UtilLogger.println("\t[VNode]:"+vNode.toString()+" Hash:"+vNode.hashFNV1_32());
            }
        }
        return this;
    }

    public void removeNode(String ip,String port) {
        Node node = new Node(ip, port);
        for(int i = 0;i<VIRTUAL_NODE_NUMBER;i++) {
            VNode vNode = node.createVNode(i);
            circle.remove(vNode.hashFNV1_32());
        }
        circle.remove(node.hashFNV1_32());
    }

    public VNode getNode(String ip, int port) {
        return getNode(ip, String.valueOf(port));
    }

    public VNode getNode(String ip, String port) {
        Node node = new Node(ip, port);
        int hash = node.hashFNV1_32();
        if(circle.isEmpty()) return null;
        SortedMap<Integer, VNode> tailMap = circle.tailMap(hash);
        int hashKey;
        if (tailMap.isEmpty()) {
            hashKey = circle.firstKey();
        }else {
            hashKey = tailMap.firstKey();
        }//顺时针最近节点
        VNode vNode = circle.get(hashKey);
        UtilLogger.println(String.format("[%s]:%s ==> [%s]:%s",
                node.hashFNV1_32(),node,vNode.hashFNV1_32(),vNode));
        return vNode;
    }

    /**
     * 第个节点都是一个服务器主机
     */
    public class Node {
        String ip;
        String port;

        public Node(String ip, String port) {
            this.ip = ip;
            this.port = port;
        }

        public String getIp() {
            return ip;
        }

        public void setIp(String ip) {
            this.ip = ip;
        }

        public String getPort() {
            return port;
        }

        public void setPort(String port) {
            this.port = port;
        }

        public VNode createVNode(int vnNumber) {
            return new VNode(ip, port, vnNumber);
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Node vNode = (Node) o;
            return Objects.equals(ip, vNode.ip) &&
                    Objects.equals(port, vNode.port);
        }

        @Override
        public String toString() {
            return ip + ":" + port;
        }

        /**
         *使用FNV1_32_HASH算法计算服务器的Hash值,这里不能重写hashCode的方法
         */
        public int hashFNV1_32(){
            String str = UtilMD5.MD5(this.toString());
            final int p = 16777619;
            int hash = (int)2166136261L;
            for (int i = 0; i < str.length(); i++)
                hash = (hash ^ str.charAt(i)) * p;
            hash += hash << 13;
            hash ^= hash >> 7;
            hash += hash << 3;
            hash ^= hash >> 17;
            hash += hash << 5;

            // 如果算出来的值为负数则取其绝对值
            if (hash < 0)
                hash = Math.abs(hash);
            return hash;
        }
    }

    /**
     * 虚拟节点
     */
    public class VNode extends Node{
        int number;

        public VNode(String ip, String port,int number) {
            super(ip, port);
            this.number = number;
        }

        public Node toNode() {
            return new Node(ip,port);
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            if (!super.equals(o)) return false;
            VNode vNode = (VNode) o;
            return number == vNode.number;
        }

        @Override
        public int hashCode() {
            return Objects.hash(number);
        }

        @Override
        public String toString() {
            return ip + ":" + port+"#"+number;
        }
    }

    /**
     * 校验hash分布均匀性
     * @return
     */
    public float check() {
        Set<Integer> ks = circle.keySet();
        int size = ks.size();
        long sum = 0L;
        for (int hash : ks) {
            sum += hash;
        }
        double percent = size == MIN_NODE_NUMBER ? MIN_NODE_NUMBER :
                (100*2*sum/size)/MAX_NODE_NUMBER;
        return Float.valueOf(String.format("%.2f", percent));
    }

    public static void main(String[] args) {
        UtilElapsedTime.test(() -> {
            ConsistentHashing ch = ConsistentHashing.build(3);
            //添加节点
            UtilLogger.println("------------添加节点----------------");
            ch.addNode("10.96.74.187", 80);
            ch.addNode("127.0.0.1", 8080);
            ch.addNode("243.15.155.0", 2150);
            ch.addNode("243.15.155.1", 2150);

            UtilLogger.println("------------是否均匀----------------");
            UtilLogger.println(ch.check() + "%");

            //获取节点
            UtilLogger.println("------------获取节点----------------");
            ch.getNode("10.96.74.187", 80);
            ch.getNode("123.1.122.253", 44);
            ch.getNode("234.67.80.219", 3306);
            return "耗时计算完成";
        });
    }

}

2.结果

------------添加节点----------------
[Node]:10.96.74.187:80 Hash:1695118842
	[VNode]:10.96.74.187:80#0 Hash:1661313686
	[VNode]:10.96.74.187:80#1 Hash:1283046442
	[VNode]:10.96.74.187:80#2 Hash:564332117
[Node]:127.0.0.1:8080 Hash:678080562
	[VNode]:127.0.0.1:8080#0 Hash:1731933288
	[VNode]:127.0.0.1:8080#1 Hash:1369405387
	[VNode]:127.0.0.1:8080#2 Hash:200594664
[Node]:243.15.155.0:2150 Hash:1175061629
	[VNode]:243.15.155.0:2150#0 Hash:134880260
	[VNode]:243.15.155.0:2150#1 Hash:1677894747
	[VNode]:243.15.155.0:2150#2 Hash:522817245
[Node]:243.15.155.1:2150 Hash:1305999210
	[VNode]:243.15.155.1:2150#0 Hash:1193457699
	[VNode]:243.15.155.1:2150#1 Hash:279279823
	[VNode]:243.15.155.1:2150#2 Hash:2115663065
------------是否均匀----------------
98.0%
------------获取节点----------------
[1695118842]:10.96.74.187:80 ==> [1731933288]:127.0.0.1:8080#0
[601034131]:123.1.122.253:44 ==> [1193457699]:243.15.155.1:2150#0
[508181784]:234.67.80.219:3306 ==> [522817245]:243.15.155.0:2150#2
[23.104187ms] 耗时计算完成

Process finished with exit code 0

3.注意事项

代码中用到了几个工具类UtilMD5,UtilLogger换成自己的即可,UtilElapsedTime用于计算耗时,可以直接去掉。

4.参考链接

对一致性Hash算法，Java代码实现的深入研究

白话解析：一致性哈希算法 consistent hashing