public function open($savePath, $sessionName)
    {
        if (!isset($this->_lifeTime)) $this->_lifeTime = intval(ini_get("session.gc_maxlifetime"));
        if (!isset($this->_refreshTime)) $this->_refreshTime = ceil($this->_lifeTime / 3);

        $this->_initSessionData = null;

        $this->_memcache = new Memcache();
        if (Kwf_Cache_Simple::$memcacheHost) {
            $servers = array(
                array(
                    'host' => Kwf_Cache_Simple::$memcacheHost,
                    'port' => Kwf_Cache_Simple::$memcachePort
                )
            );
        } else {
            throw new Kwf_Exception("no memcache configured");
        }
        foreach ($servers as $s) {
            if (version_compare(phpversion('memcache'), '2.1.0') == -1 || phpversion('memcache')=='2.2.4') { // < 2.1.0
                $this->_memcache->addServer($s['host'], $s['port'], true, 1, 1, 1);
            } else if (version_compare(phpversion('memcache'), '3.0.0') == -1) { // < 3.0.0
                $this->_memcache->addServer($s['host'], $s['port'], true, 1, 1, 1, true, null, 10000);
            } else {
                $this->_memcache->addServer($s['host'], $s['port'], true, 1, 1, 1);
            }
        }

        return true;
    }