$config['cache']['enabled'] = true;
$config['cache']['frontend'] = 'Core';
$config['cache']['frontendOptions']['cache_id_prefix'] = 'xf_';

$config['cache']['cacheSessions'] = true;

$config['cache']['backend'] = 'Memcached';
$config['cache']['backendOptions'] = array(
	'compression' => false,
	'servers' => array(
		array(
			// your memcached server IP /address
			'host' => 'localhost',
			
			// memcached port
			'port' => 11211,
		)
	)
);