(PECL memcached >= 0.1.0)
Memcached::getDelayedByKey — Request multiple items from a specific server
$server_key
   , array $keys
   [, bool $with_cas
   [, callable $value_cb
  ]] )
   Memcached::getDelayedByKey() is functionally equivalent to
   Memcached::getDelayed(), except that the free-form
   server_key can be used to map the
   keys to a specific server.
  
server_keyThe key identifying the server to store the value on.
keysArray of keys to request.
with_casWhether to request CAS token values also.
value_cb
       The result callback or NULL.
      
   Returns TRUE on success or FALSE on failure.
   Use Memcached::getResultCode() if necessary.