Memcache::add() stores variable var with key only if such key doesn't exist at the server yet. Also you can use memcache_add() function.
The key that will be associated with the item.
The variable to store. Strings and integers are stored as is, other types are stored serialized.
MEMCACHE_COMPRESSED to store the item
compressed (uses zlib).
Expiration time of the item. If it's equal to zero, the item will never expire. You can also use unix timestamp or a number of seconds starting from current time, but in the latter case the number of seconds may not exceed 2592000 (30 days).
FALSE if such key already exist. For the rest
Memcache::add() behaves similarly to