connection from connection pool uses too much memory during the time

Hello,

I've come across this problem: We have some tomcats connecting to
postgresql database using connection pools, which means, that connection
gets open while tomcat first uses it and then stays open, until we stop
tomcat. So far everything is fine, connection pooling works nicely. But.
We have some complex queries, that probably use n times allowed
work_mem. It is still not problem for us. The problem is that it looks
like, that once the open connection takes some memory, it never gives
that memory back, which ends up with our server swapping large amounts
of memory.

Am i right or wrong with my assumption?
Can i somehow force open connection to release its memory? (connection
is in the idle state most of the time).

Any other hints?

Thank you,
Honza Novak