看结果可知:一开始添加到9个客户端,连接到主机s1,s2,s3,s4的客户端分别有3,3,3,0个,经过删除主机s2,添加主机s5,最后9个客户端分别连接到主机s1,s2,s3,s4,s5的个数为4,0,1,2,2.这里要说明一下删除主机s2的情况,hash尾号为9995的客户端先连接到s2,再连接到s1,为什么会出现这种情况呢?因为每一个真实主机有n个虚拟主机,删除s2却打印“hash(7274050343425899995)改变到->s2-192.168.1.2”是因为删除了s2的其中一个虚拟主机,跳转到另一个虚拟主机,但还是在s2上,当然,这里是打印中间情况,以便了解,真实的环境是删除了s2后,所有他的虚拟节点都会马上被删除,虚拟节点上的连接也会重新连接到另一个主机的虚拟节点,不会存在这种中间情况。
以下给出所有的实现代码,大家共同学习:
public class Shard<Node> { // S类封装了机器节点的信息 ,如name、password、ip、port等 static private TreeMap<Long, Node> nodes; // 虚拟节点到真实节点的映射 static private TreeMap<Long,Node> treeKey; //key到真实节点的映射 static private List<Node> shards = new ArrayList<Node>(); // 真实机器节点 private final int NODE_NUM = 100; // 每个机器节点关联的虚拟节点个数 boolean flag = false; public Shard(List<Node> shards) { super(); this.shards = shards; init(); } public static void main(String[] args) { // System.out.println(hash("w222o1d")); // System.out.println(Long.MIN_VALUE); // System.out.println(Long.MAX_VALUE); Node s1 = new Node("s1", "192.168.1.1"); Node s2 = new Node("s2", "192.168.1.2"); Node s3 = new Node("s3", "192.168.1.3"); Node s4 = new Node("s4", "192.168.1.4"); Node s5 = new Node("s5","192.168.1.5"); shards.add(s1); shards.add(s2); shards.add(s3); shards.add(s4); Shard<Node> sh = new Shard<Shard.Node>(shards); System.out.println("添加客户端,一开始有4个主机,分别为s1,s2,s3,s4,每个主机有100个虚拟主机:"); sh.keyToNode("101客户端"); sh.keyToNode("102客户端"); sh.keyToNode("103客户端"); sh.keyToNode("104客户端"); sh.keyToNode("105客户端"); sh.keyToNode("106客户端"); sh.keyToNode("107客户端"); sh.keyToNode("108客户端"); sh.keyToNode("109客户端"); sh.deleteS(s2); sh.addS(s5); System.out.println("最后的客户端到主机的映射为:"); printKeyTree(); } public static void printKeyTree(){ for(Iterator<Long> it = treeKey.keySet().iterator();it.hasNext();){ Long lo = it.next(); System.out.println("hash("+lo+")连接到主机->"+treeKey.get(lo)); } } private void init() { // 初始化一致性hash环 nodes = new TreeMap<Long, Node>(); treeKey = new TreeMap<Long, Node>(); for (int i = 0; i != shards.size(); ++i) { // 每个真实机器节点都需要关联虚拟节点 final Node shardInfo = shards.get(i); for (int n = 0; n < NODE_NUM; n++) // 一个真实机器节点关联NODE_NUM个虚拟节点 nodes.put(hash("SHARD-" + shardInfo.name + "-NODE-" + n), shardInfo); } } //增加一个主机 private void addS(Node s) { System.out.println("增加主机"+s+"的变化:"); for (int n = 0; n < NODE_NUM; n++) addS(hash("SHARD-" + s.name + "-NODE-" + n), s); } //添加一个虚拟节点进环形结构,lg为虚拟节点的hash值 public void addS(Long lg,Node s){ SortedMap<Long, Node> tail = nodes.tailMap(lg); SortedMap<Long,Node> head = nodes.headMap(lg); Long begin = 0L; Long end = 0L; SortedMap<Long, Node> between; if(head.size()==0){ between = treeKey.tailMap(nodes.lastKey()); flag = true; }else{ begin = head.lastKey(); between = treeKey.subMap(begin, lg); flag = false; } nodes.put(lg, s); for(Iterator<Long> it=between.keySet().iterator();it.hasNext();){ Long lo = it.next(); if(flag){ treeKey.put(lo, nodes.get(lg)); System.out.println("hash("+lo+")改变到->"+tail.get(tail.firstKey())); }else{ treeKey.put(lo, nodes.get(lg)); System.out.println("hash("+lo+")改变到->"+tail.get(tail.firstKey())); } } } //删除真实节点是s public void deleteS(Node s){ if(s==null){ return; } System.out.println("删除主机"+s+"的变化:"); for(int i=0;i<NODE_NUM;i++){ //定位s节点的第i的虚拟节点的位置 SortedMap<Long, Node> tail = nodes.tailMap(hash("SHARD-" + s.name + "-NODE-" + i)); SortedMap<Long,Node> head = nodes.headMap(hash("SHARD-" + s.name + "-NODE-" + i)); Long begin = 0L; Long end = 0L; SortedMap<Long, Node> between; if(head.size()==0){ between = treeKey.tailMap(nodes.lastKey()); end = tail.firstKey(); tail.remove(tail.firstKey()); nodes.remove(tail.firstKey());//从nodes中删除s节点的第i个虚拟节点 flag = true; }else{ begin = head.lastKey(); end = tail.firstKey(); tail.remove(tail.firstKey()); between = treeKey.subMap(begin, end);//在s节点的第i个虚拟节点的所有key的集合 flag = false; } for(Iterator<Long> it = between.keySet().iterator();it.hasNext();){ Long lo = it.next(); if(flag){ treeKey.put(lo, tail.get(tail.firstKey())); System.out.println("hash("+lo+")改变到->"+tail.get(tail.firstKey())); }else{ treeKey.put(lo, tail.get(tail.firstKey())); System.out.println("hash("+lo+")改变到->"+tail.get(tail.firstKey())); } } } } //映射key到真实节点 public void keyToNode(String key){ SortedMap<Long, Node> tail = nodes.tailMap(hash(key)); // 沿环的顺时针找到一个虚拟节点 if (tail.size() == 0) { return; } treeKey.put(hash(key), tail.get(tail.firstKey())); System.out.println(key+"(hash:"+hash(key)+")连接到主机->"+tail.get(tail.firstKey())); } /** * MurMurHash算法,是非加密HASH算法,性能很高, * 比传统的CRC32,MD5,SHA-1(这两个算法都是加密HASH算法,复杂度本身就很高,带来的性能上的损害也不可避免) * 等HASH算法要快很多,而且据说这个算法的碰撞率很低. * http://murmurhash.googlepages.com/ */ private static Long 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); // for big-endian version, do this first: // finish.position(8-buf.remaining()); finish.put(buf).rewind(); h ^= finish.getLong(); h *= m; } h ^= h >>> r; h *= m; h ^= h >>> r; buf.order(byteOrder); return h; } static class Node{ String name; String ip; public Node(String name,String ip) { this.name = name; this.ip = ip; } @Override public String toString() { return this.name+"-"+this.ip; } } }