pgmemcache: PostgreSQL memcache function

memcache_add(key::TEXT, value::TEXT, expire::TIMESTAMPTZ)
memcache_add(key::TEXT, value::TEXT, expire::INTERVAL)
memcache_add(key::TEXT, value::TEXT)

Adds a key to the cache cluster, if the key does not already exist.

newval = memcache_decr(key::TEXT, decrement::INT8)
newval = memcache_decr(key::TEXT)

If key exists and is an integer, atomically decrements by the value specified (default decrement is one). Returns INT value after decrement.