(PECL memcached >= 0.1.0)
Memcached::addServer — Add a server to the server pool
$host
   , int $port
   [, int $weight = 0
  ] )
   Memcached::addServer() adds the specified server to the
   server pool. No connection is established to the server at this time, but
   if you are using consistent key distribution option (via
   Memcached::DISTRIBUTION_CONSISTENT or
   Memcached::OPT_LIBKETAMA_COMPATIBLE), some of the
   internal data structures will have to be updated. Thus, if you need to add
   multiple servers, it is better to use
   Memcached::addServers() as the update then happens
   only once.
  
   The same server may appear multiple times in the server pool, because no
   duplication checks are made. This is not advisable; instead, use the
   weight option to increase the selection weighting of
   this server.
  
host
       The hostname of the memcache server. If the hostname is invalid,
       data-related operations will set 
       Memcached::RES_HOST_LOOKUP_FAILURE result code. As
       of version 2.0.0b1, this parameter may also specify the path of a unix
       socket filepath ex. /path/to/memcached.sock
       to use UNIX domain sockets, in this case port
       must also be set to 0.
      
portThe port on which memcache is running. Usually, this is 11211. As of version 2.0.0b1, set this parameter to 0 when using UNIX domain sockets.
weightThe weight of the server relative to the total weight of all the servers in the pool. This controls the probability of the server being selected for operations. This is used only with consistent distribution option and usually corresponds to the amount of memory available to memcache on that server.
   Returns TRUE on success or FALSE on failure.
  
Example #1 Memcached::addServer() example
<?php
$m = new Memcached();
/* Add 2 servers, so that the second one
   is twice as likely to be selected. */
$m->addServer('mem1.domain.com', 11211, 33);
$m->addServer('mem2.domain.com', 11211, 67);
?>