Alvaro Herrera wrote:
There are two additional patches in the VACUUM code.  One is Heikki's
patch to recalculate OldestXmin in the vacuum run.
(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":

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

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