Re: Remaining VACUUM patches

Alvaro Herrera wrote:
> There are two additional patches in the VACUUM code. One is Heikki's
> patch to recalculate OldestXmin in the vacuum run.
>
> http://groups.google.es/group/pgsql.patches/browse_thread/thread/b2cfc901534d8990/40ba5b2fbb8f5b91
> (much nicer than our archives because the whole thread is there, not
> just month-sized pieces).
>
> That thread ended without any conclusion; it is said that the patch will
> be reconsidered when Simon Riggs' patch about the WAL flushing bug
> lands, but I don't know what patch is that. Is it in the patch queue?
> Was it already applied?

It's in patch queue, not applied. It's the one with title "Bug: Buffer
cache is not scan resistant":
http://momjian.us/mhonarc/patches/msg00048.html

> The problem with the patch is that the DBT-2 test showed decreased
> performance, but that was still under investigation.
>
> What is the status of this?

The plan is that I'll rerun the DBT-2 test after the above patch is
applied. After that we'll decide if we want the OldestXmin patch or not.

> The other patch was ITAGAKI Takahiro's patch to fix n_dead_tuples in
> pgstats after VACUUM when there is concurrent update activity. This
> patch is still on hold largely because the above patch would cause it to
> be a bit obsolete. So I think if we're not going to apply the former,
> we should apply this one.

I'd like to have the "buffer cache is not scan resistant" patch reviewed
first to get the ball rolling on these other patches. The vacuum-related
patches are just small tweaks, and they don't conflict with any of the
bigger patches in the queue, so there's no reason to rush them,

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com