memcache客户端实现集群之一致性hash算法

一致性哈希的算法把取余算法的等于号来选择mem服务器变成了大于号来选择mem服务器，这应该是才是关键，可以使一个键的mem服务器落点变成是动态选择（一个服务器down掉然后选择crc32(key)后大于这个服务器的落点....）

添加虚拟节点，虚拟节点其实还是原来那几台服务器，每个虚拟节点都对应一个真实的服务器，起到分散节点的作用
原理如：关键点 hash环的理解和构建。

代码如下：libraries/MemCluster.php

<?php
/**
 */

//一致性hash
// 功能 添加节点；   ；根据用户数据key  获取应该使用那台node
class MemCluster
{
    protected $nodes = array();
    protected $position = array();
    protected $virtualNum=32;  //每个节点有32个虚拟节点；具体数量也可以 16 ，8等


    public function hash($str){
        //将字符串转成32位符号整数
        return sprintf("%u", crc32($str));
    }

    //查找key 落到哪个节点上
    public function findNode($key){
        $point = $this->hash($key);

        //先取圆环上最小的一个节点
        //$key 哈希后比最大的节点都大就放到第一个节点
        $node = current($this->position);

        //下面这个查找可以  后期优化为二分查找法。
        foreach($this->position as $k=>$v){
            if($point <= $k){
                $node = $v;
                break;
            }
        }

        //复位数组指针
        reset($this->position);
        return $node;
    }

    public function addNode($node){
        if(isset($this->nodes[$node])){
            return;
        }

        for($i=0; $i<$this->virtualNum; $i++){
            $pos = $this->hash($node.'-'.$i);
            $this->position[$pos] = $node;

            //方便删除对应的虚拟节点
            $this->nodes[$node][] = $pos;
        }

        $this->sortPos();
    }

    public function delNode($node){
        if(!isset($this->nodes[$node])){
            return;
        }

        //删除对应的虚拟节点
        foreach($this->nodes[$node] as $k){
            unset($this->position[$k]);
        }
        unset($this->nodes[$node]);

    }

    protected function sortPos(){
        //正常比较单元，不改变类型
        ksort($this->position, SORT_REGULAR);
    }
}

测试代码如下：contoller/Mem.php

	public function test(){

	    $this->load->library('memcluster');

	    $memServerArr = array('192.168.0.1:6666', '192.168.0.2:8888', '192.168.0.3:9999');
	    foreach ($memServerArr as $mem){
	        $this->memcluster->addNode($mem);
        }

	    $key = "goods:1688";
	    $memNode = $this->memcluster->findNode($key);
	    echo $memNode,"<br/>";

        $key = "goods:1689";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";

        $key = "goods:1670";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";

        $key = "goods:1671";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";

        $key = "goods:1672";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";

        $key = "goods:1673";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";

        $key = "order:1673";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";

        $key = "order:1674";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";

        $key = "order:1675";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";

        $key = "post:1675";
        $memNode = $this->memcluster->findNode($key);
        echo $memNode,"<br/>";
    }

memcache客户端实现集群之一致性hash算法

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