Memcache::add() stores variable
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.
Use 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).
Returns TRUE on success or FALSE on failure.
Returns FALSE if such key already exist. For the rest
Memcache::add() behaves similarly to