class FlexHash{
    private $server_list = array();
    private $is_sort = false;
    public function add_server($server)
    {
        $hash = mhash(MHASH_MD5,$server);
        if(!isset($this->server_list[$hash])){
            $this->server_list[$hash] = $server;
        }
        $this->is_sort = false;
        return true;
    }
    public function remove_server($server)
    {
        $hash = mhash(MHASH_MD5,$server);
        if(isset($this->server_list[$hash])){
             unset($this->server_list[$hash]);
        }
        $this->is_sort = false;
        return true;
    }
    public function look_up($key)
    {
        $hash = mhash(MHASH_MD5,$key);
        if(!$this->is_sort){
            krsort($this->server_list,SORT_NUMERIC);
            $this->is_sort = true;
        }

        foreach ($this->server_list as $item => $value) {
            if($hash >= $value) return $value;
        }

        return $this->server_list[count($this->server_list) - 1];
    }
}

//echo $hash = mhash(MHASH_MD5,'1.2.3.4');

$server = new FlexHash();
$server->add_server('1.2.3.4');
$server->add_server('5.6.7.8');
$server->add_server('9.10.11.12');
$server->add_server('13.14.15.16');
$server->add_server('17.18.19.20');
$server->add_server('21.22.23.24');
$server->add_server('25.26.27.28');

echo "save 1 in ".$server->look_up('key1')."<br>";
echo "save 2 in ".$server->look_up('key2')."<br>";

$server->remove_server("21.22.23.24");
echo "save 1 in ".$server->look_up('key1')."<br>";
echo "save 2 in ".$server->look_up('key2')."<br>";

$server->add_server('29.30.31.32');
echo "save 1 in ".$server->look_up('key1')."<br>";
echo "save 2 in ".$server->look_up('key2')."<br>";
 

簡單記錄下實現的類，各位有則取之。