memcache一致性hash的php實現方法,memcachehash

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memcache一致性hash的php實現方法,memcachehash
最近在看一些分布式方面的文章,所以就用php實現一致性hash來練練手,以前一般用的是最原始的hash模數做 分布式,當生產過程中添加或刪除一台memcache都會造成資料的全部失效,一致性hash就是為瞭解決這個問題,把失效資料降到最低,相關資料可以 google一下!

php實現效率有一定的缺失,如果要高效率,還是寫擴充比較好

經測試,5個memcache,每個memcache產生100個虛擬節點,set加get1000次,與單個memcache直接set加get慢5倍,所以效率一般,有待最佳化!

在閱讀本文之前,最好知道二分尋找法。


實現過程:


memcache的配置 ip+連接埠+虛擬節點序號 做hash,使用的是crc32,形成一個閉環。

對要操作的key進行crc32

二分法在虛擬節點環中尋找最近的一個虛擬節點

從虛擬節點中提取真實的memcache ip和連接埠,做單例串連


<?php /**      * memcache一致性hash的php實現方法     * @author http://www.lai18.com     * @date 2015-04-19      */class memcacheHashMap {        private $_node = array();        private $_nodeData = array();        private $_keyNode = 0;        private $_memcache = null;        //每個物理伺服器產生虛擬節點個數 [註:節點數越多,cache分布的均勻性越好,同時set get操作時,也更耗資源,10台物理伺服器,採用200較為合理]        private $_virtualNodeNum = 200;        private function __construct() {                $config = array(//五個memcache伺服器                                                '127.0.0.1:11211',                                                '127.0.0.1:11212',                                                '127.0.0.1:11213',                                                '127.0.0.1:11214',                                                '127.0.0.1:11215'                                        );                if (!$config) throw new Exception('Cache config NULL');                foreach ($config as $key => $value) {                        for ($i = 0; $i < $this->_virtualNodeNum; $i++) {                                $this->_node[sprintf("%u", crc32($value . '_' . $i))] = $value . '_' . $i;//迴圈為每個memcache伺服器建立200個虛擬節點                        }                }                ksort($this->_node);//建立出來的1000個虛擬節點按照鍵名從小到大排序        }        //執行個體化該類        static public function getInstance() {                static $memcacheObj = null;                if (!is_object($memcacheObj)) {                        $memcacheObj = new self();                }                return $memcacheObj;        }        //根據傳來的鍵尋找到對應虛擬節點的位置        private function _connectMemcache($key) {                $this->_nodeData = array_keys($this->_node);//所有的虛擬節點的鍵的數組                $this->_keyNode = sprintf("%u", crc32($key));//算出鍵的hash值                $nodeKey = $this->_findServerNode();//找出對應的虛擬節點                //如果超出環,從頭再用二分法尋找一個最近的,然後環的頭尾做判斷,取最接近的節點                if ($this->_keyNode > end($this->_nodeData)) {                        $this->_keyNode -= end($this->_nodeData);                        $nodeKey2 = $this->_findServerNode();                        if (abs($nodeKey2 - $this->_keyNode) < abs($nodeKey - $this->_keyNode))  $nodeKey = $nodeKey2;                }                var_dump($this->_node[$nodeKey]);                list($config, $num) = explode('_', $this->_node[$nodeKey]);                if (!$config) throw new Exception('Cache config Error');                if (!isset($this->_memcache[$config])) {                        $this->_memcache[$config] = new Memcache;                        list($host, $port) = explode(':', $config);                        $this->_memcache[$config]->connect($host, $port);                }                return $this->_memcache[$config];        }        //二分法根據給出的值找出最近的虛擬節點位置        private function _findServerNode($m = 0, $b = 0) {            $total = count($this->_nodeData);            if ($total != 0 && $b == 0) $b = $total - 1;            if ($m < $b){                $avg = intval(($m+$b) / 2);                if ($this->_nodeData[$avg] == $this->_keyNode) return $this->_nodeData[$avg];                elseif ($this->_keyNode < $this->_nodeData[$avg] && ($avg-1 >= 0)) return $this->_findServerNode($m, $avg-1);                else return $this->_findServerNode($avg+1, $b);            }                if (abs($this->_nodeData[$b] - $this->_keyNode) < abs($this->_nodeData[$m] - $this->_keyNode))  return $this->_nodeData[$b];                else return $this->_nodeData[$m];        }        public function set($key, $value, $expire = 0) {                return $this->_connectMemcache($key)->set($key, json_encode($value), 0, $expire);        }        public function add($key, $value, $expire = 0) {                return $this->_connectMemcache($key)->add($key, json_encode($value), 0, $expire);        }        public function get($key) {                return json_decode($this->_connectMemcache($key)->get($key), true);        }        public function delete($key) {                return $this->_connectMemcache($key)->delete($key);        }}$runData['BEGIN_TIME'] = microtime(true);//測試一萬次set加getfor($i=0;$i<10000;$i++) {        $key = md5(mt_rand());        $b = memcacheHashMap::getInstance()->set($key, time(), 10);}var_dump(number_format(microtime(true) - $runData['BEGIN_TIME'],6));$runData['BEGIN_TIME'] = microtime(true); $m= new Memcache;$m->connect('127.0.0.1', 11211);for($i=0;$i<10000;$i++) {        $key = md5(mt_rand());        $b = $m->set($key, time(), 0, 10);}var_dump(number_format(microtime(true) - $runData['BEGIN_TIME'],6));?>


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