<?php/** * 一致性hash分布式算法 * @param $key * @return int * 實現步驟 * 1.先將0~ 是32位最大帶符號整數（0x7FFFFFFF） 想象成一個閉環 * 2.將服務器列表通過hash算法分布在 圓環之中 * 3.將key值也分布在圓環之中 * 4.通過_isSorted判斷服務器是否需要進行倒序排序 排序后遍歷服務器 找到最近的服務器 返回 * hash算法是不保證平衡的 為了盡量保證平衡性 我們應該加入虛擬節點數 將一個服務器節點虛擬化成為多個 較大程度上保證了平衡性 */class FlexiHash{  private $_serverList = array();  private $_isSorted = false;  private $_virtual_node_num = 20;//虛擬節點數 服務器越少 增加的虛擬節點數應該越多  //通過hash算法返回一個整數值  protected function myHash($key){    $md5 = substr(md5($key),0,8);    $seed = 31; //種子值    $hash=0;    for($i=0;$i<8;$i++){      $hash = $hash*$seed+ord($md5{$i}); //ord 返回ascii值      $i++;    }    return $hash&0x7FFFFFFF; //0x7FFFFFFF表示最大值  }  //添加服務器  function addServer($server){    $hash =$this->myHash($server. '#1');    if(!isset($this->_serverList[$hash])) {      for ($i = 1; $i <= $this->_virtual_node_num; $i++) {        $hash = $this->myHash($server . '#' . $i);        $this->_serverList[$hash] = $server;      }    }    $this->_isSorted = false;    return true;  }  //刪除服務器  function removeServer($server){    for ($i = 1; $i <= $this->_virtual_node_num; $i++) {      $hash = $this->myHash($server . '#' . $i);      unset($this->_serverList[$hash]);    }    $this->_isSorted = false;    return true;  }  //獲取服務器  function lookup($key){    $hash =$this->myHash($key);    if(!$this->_isSorted){      krsort($this->_serverList,SORT_NUMERIC);      $this->_isSorted = true;    }    foreach($this->_serverList as $pos=>$server){      if($hash >= $pos) return $server;    }    return end($this->_serverList);  }  public function getServerList(){    krsort($this->_serverList,SORT_NUMERIC);    return $this->_serverList;  }}//demo test$hserver = new FlexiHash();//添加服務器$hserver->addServer('192.168.1.1');$hserver->addServer('192.168.1.2');$hserver->addServer('192.168.1.3');$hserver->addServer('192.168.1.4');$hserver->addServer('192.168.1.5');$key1='Key1111';$key2='Key2222';$key2='Key3333';$key2='Key4444';$key2='Key5555';$key2='Key6666';echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;echo "================================================".PHP_EOL;//移除服務器 key值將自動轉義到下一臺服務器$hserver->removeServer('192.168.1.4');echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;echo "================================================".PHP_EOL;//恢復故障服務器 key值將恢復原來服務器$hserver->addServer('192.168.1.4');echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;