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From: Sami Imseih <samimseih@gmail.com>
Date: Thu, 20 Nov 2025 10:34:14 -0600
Message-ID: 
 <CAA5RZ0vJH5k+tWbCG-tLfSCb7=jngwLkQHdwPLo8gP92mg2i_g@mail.gmail.com>
Subject: Re: another autovacuum scheduling thread
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Robert Treat <rob@xzilla.net>,
	David Rowley <dgrowleyml@gmail.com>,
 Jeremy Schneider <schneider@ardentperf.com>,
	pgsql-hackers@postgresql.org
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> On Thu, Nov 20, 2025 at 09:30:42AM -0500, Robert Haas wrote:
> > Point being: I think we need to avoid the mindset that we can't be
> > stupider than we are now. I don't think there's any way we would
> > commit something that is GENERALLY stupider than we are now, but it's
> > not about averages. It's about whether there are specific cases that
> > are common enough to worry about which end up getting regressed. I'm
> > honestly not sure how much of a risk that is, and, again, I'm not
> > trying to kill the patch. It might well be that the patch is already
> > good enough that such scenarios will be extremely rare. However, it's
> > easy to get overconfident when replacing a completely unintelligent
> > system with a smarter one. The risk of something backfiring can
> > sometimes be higher than one anticipates.
>
> That's a fair point.  The possibly-entirely-theoretical case that's in my
> head is when your oldest and lowest-OID table is also the biggest and most
> active.  That seems like it could be a popular pattern in the field, and it
> probably benefits to some degree from the sequential scan returning it
> earlier.  I don't know how much to worry about stuff like this.

I think it would be difficult to introduce this new prioritization
system without a
GUC to control the prioritization behavior. Since ordering by pg_class has been
the only behavior ever since autovacuum was released, there should be a way
for users to revert back to this. The default could be the new
prioritization strategy.

Introducing new GUCs is something to be avoided if possible, but I think this
case is a clear one to me.

--
Sami Imseih
Amazon Web Services (AWS)