一致性哈希实现

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);
}
}

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一致性哈希实现