private function connect()
    {
        $memcache = new Memcached();
        $memcache->addServer($this->host, $this->port);

        if (null !== $this->prefix) {
            $memcache->setOption(Memcached::OPT_PREFIX_KEY, $this->prefix);
        }

        $this->memcached = $memcache;
    }