Message-ID: <2383464d102aa6e16ff477837878aa2beb7e3e3b.camel@cybertec.at>
Subject: Re: vacuum an all frozen table
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Senor Cervesa <frio_cervesa@hotmail.com>, 
	"pgsql-general@lists.postgresql.org"
	 <pgsql-general@lists.postgresql.org>
Date: Wed, 22 May 2024 09:34:47 +0200
In-Reply-To: <SN4P221MB0683A34E144BD9A66BBCB566F7EA2@SN4P221MB0683.NAMP221.PROD.OUTLOOK.COM>
References: 
	<SN4P221MB0683A34E144BD9A66BBCB566F7EA2@SN4P221MB0683.NAMP221.PROD.OUTLOOK.COM>
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On Tue, 2024-05-21 at 14:46 -0700, Senor Cervesa wrote:
> I'd like to understand what's happening here and whether there is=20
> anything I can do to improve the situation.
>=20
> PostgreSQL v11.22 (yeah, I know. Needs upgrade)
>=20
> The following 3 autovacuum log entries show a vacuum of an append only=
=20
> table that has not had any changes since the end of 5/10/2024. There is=
=20
> only 1 page not skipped in each instance yet it takes over 1100 seconds=
=20
> to complete. Visibility map shows all frozen. The associated TOAST table=
=20
> is similar in numbers except that it completes in sub-second times.
>=20
> I understand that the vacuum is occurring due to age of=20
> pg_class.relfrozenxid for the table but what exactly is it referring to=
=20
> in these cases? Can that also be frozen or similar? Should I add=20
> autovacuum_freeze_max_age=3D400000000 or higher to relopts do reduce=20
> vacuum frequency.
>=20
>=20
> 2024-05-17 09:56:57.167 GMT "" "" LOG:=C2=A0 automatic aggressive vacuum =
of=20
> table "workdb1.public.log_entry_20240510": index scans: 0
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pages: 0 removed, 535517=
48 remain, 0 skipped due to pins,=20
> 53551747 skipped frozen
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 tuples: 0 removed, 24238=
4013 remain, 0 are dead but not yet=20
> removable, oldest xmin: 3245896267
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 buffer usage: 107117593 =
hits, 123159244 misses, 3 dirtied
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 avg read rate: 856.853 M=
B/s, avg write rate: 0.000 MB/s
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 system usage: CPU: user:=
 151.07 s, system: 638.29 s, elapsed:=20
> 1122.92 s

Strange.  Could you run

  VACUUM (VERBOSE, FREEZE) public.log_entry_20240510;

and show the result?  Perhaps that contains some clues.

Yours,
Laurenz Albe