一致性哈希实现

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发布于: 2020 年 07 月 08 日
实现一致性哈希的要点：
有一个很多slot的环
每个服务器有N个虚拟节点，分布到环上，一个虚拟节点对应一个slot
存储数据时，key的哈希值，没顺时针方向找到最近的slot（包括相等）对应的节点进行存储
哈希函数要使计算的哈希值尽量均匀分布
1、取哈希值接口
public interface IHashService {
    int hash(String key);
}
﻿
2、取哈希值实现﻿
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
public class HashService implements IHashService {
    @Override
    public int hash(String key) {
        ByteBuffer buf = ByteBuffer.wrap(key.getBytes());
        int seed = 0x1234ABCD;
        ByteOrder byteOrder = buf.order();
        buf.order(ByteOrder.LITTLE_ENDIAN);
        long m = 0xc6a4a7935bd1e995L;
        int r = 47;
        long h = seed ^ (buf.remaining() * m);
        long k;
        while (buf.remaining() >= 8) {
            k = buf.getLong();
            k *= m;
            k ^= k >>> r;
            k *= m;
            h ^= k;
            h *= m;
        }
        if (buf.remaining() > 0) {
            ByteBuffer finish = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN);
            finish.put(buf).rewind();
            h ^= finish.getLong();
            h *= m;
        }
        h ^= h >>> r;
        h *= m;
        h ^= h >>> r;
        buf.order(byteOrder);
//        return h;
        return (int)(Math.abs(h) % Integer.MAX_VALUE);
    }
}
  
3、服务器结点
public class Node {
    private String ip;
    private int port;
    public Node(String ip, int port) {
        this.ip = ip;
        this.port = port;
    }
    @Override
    public String toString() {
        return "Node{" +
                "ip='" + ip + '\'' +
                ", port=" + port +
                '}';
    }
}
﻿
4、一致性哈希
import java.util.SortedMap;
import java.util.TreeMap;
public class ConsistentHash<T> {
    /**
     * 每台服务器的slot数量
     */
    private int slotNumberPerServer;
    /**
     * 一致性哈希环
     */
    private SortedMap<Integer, T> hashCircle = new TreeMap<Integer, T>();
    /**
     * 哈希算法服务
     */
    private IHashService hashService;
    public ConsistentHash(int slotNumberPerServer,  IHashService hashService) {
        this.slotNumberPerServer = slotNumberPerServer;
        this.hashService = hashService;
    }
    public void addNode(T node) {
        for (int i = 0; i < slotNumberPerServer; i++) {
            hashCircle.put(hashService.hash(node.toString() + i), node);
        }
    }
    public void removeNode(T node) {
        for (int i = 0; i < slotNumberPerServer; i++) {
            hashCircle.remove(hashService.hash(node.toString() + i));
        }
    }
    public T getNodeByKey(String key) {
        if (hashCircle.isEmpty()) {
            return null;
        }
        int hashCode = hashService.hash(key);
        if (!hashCircle.containsKey(hashCode)) {
            SortedMap<Integer, T> tailMap = hashCircle.tailMap(hashCode);
            hashCode = tailMap.isEmpty() ? hashCircle.firstKey() : tailMap.firstKey();
        }
        return hashCircle.get(hashCode);
    }
    public static void main(String[] args) {
        System.out.println(-4 >> 2);
        System.out.println(-4 >>> 2);
    }
}
﻿
5、调用及测试﻿
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
public class Client {
    public static void main(String[] args) {
        IHashService hashService = new HashService();
        ConsistentHash<Node> nodeConsistentHash = new ConsistentHash<>(100, hashService);
        Map<Node, Integer> hitMap = new HashMap<>();
        int countNode = 10;
        for (int i = 0; i < countNode; i++) {
            Node node = new Node("192.168.1." + i, 8080);
            nodeConsistentHash.addNode(node);
            System.out.println(node.hashCode());
            hitMap.put(node, 0);
        }
        System.out.println("--------------------------------------------------------");
        long startTime = System.currentTimeMillis();
        int countKV = 1000000;
        for (int i = 0; i < countKV; i++) {
            String uuid = UUID.randomUUID().toString();
            Node node = nodeConsistentHash.getNodeByKey(uuid);
            int count = hitMap.get(node);
            hitMap.put(node, ++count);
        }
        for (Map.Entry<Node, Integer> entry : hitMap.entrySet()) {
            System.out.println(entry.toString());
        }
        System.out.println("--------------------------------------------------------");
        long spentTime = System.currentTimeMillis() - startTime;
        System.out.println(String.format("spent %s ms", spentTime));
        int averageHit = countKV / countNode;
        double temp = hitMap.values().stream().map(value -> Math.pow((value - averageHit), 2)).reduce(0.0, (s, e) -> s = s + e);
        double standardDeviation = Math.sqrt(temp/countNode);
        System.out.println("standardDeviation: " + standardDeviation);
    }
}
﻿
发布于: 2020 年 07 月 08 日阅读数: 54
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