php实现效率有一定的缺失，如果要高效率，还是写扩展比较好
经测试，5个memcache，每个memcache生成100个虚拟节点，set加get1000次，与单个memcache直接set加get慢5倍，所以效率一般，有待优化！
实现过程：

<?php/*** 一致性哈希memcache分布式，采用的是虚拟节点的方式解决分布均匀性问题,查找节点采用二分法快速查找* the last known user to change this file in the repository  <$LastChangedBy: nash.xiong [        DISCUZ_CODE_0        ]gt;* @author nash.xiong <nash.xiong@gmail.com>* @copyright Copyright &copy; 2003-2012 phpd.cn* @license */class memcacheHashMap {private $_node = array();private $_nodeData = array();private $_keyNode = 0;private $_memcache = null;//每个物理服务器生成虚拟节点个数 [注：节点数越多，cache分布的均匀性越好，同时set get操作时，也更耗资源，10台物理服务器，采用200较为合理]private $_virtualNodeNum = 200; private function __construct() {/* 放入配置文件 */$config = array('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 . '_' . $i;}}ksort($this->_node);}private function __clone(){}/*** 单例，保证只有一个实例*/static public function getInstance() {static $memcacheObj = null;if (!is_object($memcacheObj)) {$memcacheObj = new self();}return $memcacheObj;}/*** 根据key做一致性hash后连接到一台物理memcache服务器* @param string $key*/private function _connectMemcache($key) {$this->_nodeData = array_keys($this->_node);$this->_keyNode = sprintf("%u", crc32($key));$nodeKey = $this->_findServerNode();//如果超出环，从头再用二分法查找一个最近的，然后环的头尾做判断，取最接近的节点if ($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];}/*** 采用二分法从虚拟memcache节点中查找最近的节点* @param unknown_type $m* @param unknown_type $b*/private function _findServerNode($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);//测试一万次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));