(PECL memcached >= 2.0.0)
Increment numeric item's value, stored on a specific server
public int Memcached::incrementByKey ( string $server_key, string $key [, int $offset = 1 [, int $initial_value = 0 [, int $expiry = 0 ]]] )
Memcached::incrementByKey() increments a numeric item's value by the specified offset. If the item's value is not numeric, an error will result. Memcached::incrementByKey() will set the item to t