$config['cache']['enabled'] = true;
$config['cache']['frontend'] = 'Core';
$config['cache']['frontendOptions']['cache_id_prefix'] = 'xf_';
$config['cache']['cacheSessions'] = true; // Set this to false or do not set this at all if you are using APC
$config['cache']['backend'] = 'File'; // File, Apc or memcache
/**
* if your backend is memcache, add this. If not, don't.
**/
$config['cache']['backendOptions'] = array(
'compression' => false,
'servers' => array(
array(
// your memcached server IP /address
'host' => 'localhost',
// memcached port
'port' => 11211,
)
)
);