Re: First steps with 8.3 and autovacuum launcher

Michael Paesold escribió:
> Simon Riggs wrote:

> Hmm, I am not sure we are there, yet. Autovacuum does take extra care to
> vacuum tables nearing xid wrap-around, right? It even does so when
> autovacuum is disabled in the configuration.
>
> So in case a vacuum is needed for that very reason, the vacuum should *not*
> be canceled, of course. So we don't really need the information, whether
> the AV worker is doing VACUUM or ANALYZE, but whether it is critical
> against xid wrap-around. Could that be done as easily as in Alvaro's patch
> for distinguishing vacuum/analyze? Alvaro?

Yes, I think it is easy to mark the "is for xid wraparound" bit in the
WorkerInfo struct and have the cancel work only if it's off.

However, what I think should happen is that the signal handler for
SIGINT in a worker for xid wraparound should not cancel the current
vacuum. Instead turn it into a no-op, if possible. That way we also
disallow a user from cancelling vacuums for xid wraparound. I think he
can do that with pg_cancel_backend, and it could be dangerous.

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.