Session management using memcached

I'm trying to manage the session using memcached because I'm load balancing two servers.

I have added the following code to all the pages, but the loading is very heavy...

How should I change it?

Please let me know if you know more.
Thank you for your cooperation.

<?php
$mc = new Memcached();
$mc->addServer("ip address", 11211);
if(empty($_SESSION["user"])){
  if($mc->get("id")}
    $_SESSION["user"]["id"]=$mc->get("id");
  }
}