on connect/on disconnect

(this is my first post to this list...)

I am wondering if Postgres, and/or SQL in general, has a facility to
run a function at connection set-up time (after a successful connection
attempt) and/or at session completion (or disconnect)?

I want to pre-populate a table (actually an INSERT rule on a view)
with some user-specific data that is unlikely to change during the
session and which is "difficult" to process (ie. affects performance
to do it too often).

Clearly, I can do this manually anyway as the first operation after
a connection is established, but I would like also to clear it out
when the session terminates (so, I guess I am really interested in
a "trigger" of some sort on end-of-session).

Purely session/connection-based temporary tables would also do what
I need, but temporary tables don't seem to be able to work that way.

Cheers,

Bob Edwards.