Casey Duncan <casey(at)pandora(dot)com> writes:
> - The autovac daemon doesn't initiate a database-wide vacuum until
> 100,000 txns before the txn id warning hits. In my case this gives
> only a few minutes under peak load.
I believe this problem is largely addressed for 8.2; see
http://developer.postgresql.org/pgdocs/postgres/routine-vacuuming.html#VACUUM-FOR-WRAPAROUND
The default autovac interval is a lot more conservative than it was
before (200M transactions), and you can tune things if you need to.
regards, tom lane