currval sequence memory storage?

I am using jdbc against postgres 7.2.1. My tables are all designed with a
serial field as the prmiary key. When I perform inserts, I have found
through FAQ's that I can use currval to get the last value used for the
sequence that is unique to my process. My questions is, when does the memory
storage used for this currval get released and what triggers its release? If
it is never released, does that cause the process to consume excessive
memory after several inserts across multiple tables? 


Thanks,