Date: Thu, 19 Mar 2026 10:49:33 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: Greg Burd <greg@burd.me>
Cc: David Rowley <dgrowleyml@gmail.com>, Sami Imseih <samimseih@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>, Robert Treat <rob@xzilla.net>,
	Jeremy Schneider <schneider@ardentperf.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: another autovacuum scheduling thread
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On Thu, Mar 19, 2026 at 09:49:34AM -0400, Greg Burd wrote:
> My concern isn't that wraparound vacuums are inherently alarming, I agree
> with you that reaching freeze_max_age isn't a crisis. The issue is a
> scoring-scale problem in the gap between freeze_max_age (200M) and
> failsafe age (1.6B).
> 
> In that 1.4B XID window, force_vacuum tables have XID scores of 1.0–8.0
> (age/freeze_max_age), while typical active tables accumulate dead-tuple
> scores of 18–70+ within hours of their last vacuum. The exponential boost
> doesn't activate until failsafe age, so force_vacuum tables are
> systematically outranked by routine bloat cleanup for what could be days
> or weeks in production.

I think "systematically outranked" makes the problem sound worse than it
is.  Once the freeze age is reached, the table is going to get added to the
list no matter what, it just might be sorted lower.

>> Having said that, I'd not realised that Nathan capped the new GUCs at
>> 1.0. I think we should allow those to be set higher, likely at least
>> to 10.0.
> 
> That would definitely help. If autovacuum_freeze_score_weight could be
> set to 8.0–10.0, DBAs could manually restore the priority we want.

Done in the attached.

>> Maybe we could consider adjusting the code that's setting the
>> xid_score/mxid_score so that we start scaling the score aggressively
>> when if (xid_age >= effective_xid_failsafe_age /
>> Max(autovacuum_freeze_score_weight,1.0)) becomes true
> 
> This is clever, it would make the aggressive scaling kick in earlier when
> the weight is higher. At weight=8.0, you'd get exponential boost starting
> at 200M (failsafe/8) instead of 1.6B.

Seems reasonable.  I've added this, too.  Something else we might want to
consider is scaling the score once the freeze age is reached, just much
less aggressively than we do at the failsafe age.  It probably doesn't make
sense to start scaling too much at 200M, but at 1.5B, yeah, we should
probably process the table sooner than later.

-- 
nathan

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