(PECL memcached >= 0.1.0)
Memcached::casByKey — Compare and swap an item on a specific server
Memcached::casByKey() is functionally equivalent to Memcached::cas, except that the free-form server_key can be used to map the key to a specific server. This is useful if you need to keep a bunch of related keys on a certain server.
Unique value associated with the existing item. Generated by memcache.
The key identifying the server to store the value on.
The key under which to store the value.
The value to store.
The expiration time, defaults to 0. See Expiration Times for more info.
Returns TRUE on success or FALSE on failure. The Memcached::getResultCode will return Memcached::RES_DATA_EXISTS if the item you are trying to store has been modified since you last fetched it.