"Thorvald Natvig" <thorvald@medallia.com> writes:
> We get a lot of "FATAL: canceling authentication due to timeout" in the
> log, with accompanying closed connections to clients.
Well, the only known cause of that (other than genuine timeout
conditions) is in fact fixed in 9.1rc1. You have not provided any
information that would permit anyone to look for another cause.
> There does indeed seem to be a correlation between doing vacuum and seeing
> this error.
Are you doing VACUUM FULLs on pg_authid (and if so, why)? If you are,
is it possible that those are queuing up behind other queries that
access pg_authid, and for some reason aren't releasing their locks
promptly?
regards, tom lane