Re: [HACKERS] Autovacuum loose ends

On Tue, Aug 09, 2005 at 11:24:40PM -0400, Tom Lane wrote:
> Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> > Hmm. I have a patch for this, but now that it's ready, I wonder if it's
> > really needed. If I understand vacuum_set_xid_limits() correctly, it's
> > very difficult for the vacuumxid to be far behind the freeze limit.
>
> Umm ... they can be close together, or a billion XIDs apart, depending
> on whether the FREEZE option was used.

Sorry, my point was that vacuumxid is generally going to be higher than
freeze-xid, and where it isn't, a simple vacuum can't fix it.

But now that I think about it, maybe the point is that if a long-running
transaction (a billon-transactions old transaction?) was running when
the last database-wide vacuum was run, then vacuumxid is going to be
older than freeze-xid, so we may need a database-wide vacuum to fix that
even though the freeze-xid is not old enough.

Is that right?

--
Alvaro Herrera (<alvherre[a]alvh.no-ip.org>)
We take risks not to escape from life, but to prevent life escaping from us.