Message-ID: <cb0379f7690080f936541470510b94de05cf520a.camel@cybertec.at>
Subject: Re: Configure autovacuum
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: "Shenavai, Manuel" <manuel.shenavai@sap.com>, pgsql-general
	 <pgsql-general@postgresql.org>
Date: Fri, 14 Jun 2024 09:41:02 +0200
In-Reply-To: <AM9PR02MB7410C756DC2DFADC7B4E2DD6E8C22@AM9PR02MB7410.eurprd02.prod.outlook.com>
References: 
	<AM9PR02MB7410C756DC2DFADC7B4E2DD6E8C22@AM9PR02MB7410.eurprd02.prod.outlook.com>
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On Fri, 2024-06-14 at 06:20 +0000, Shenavai, Manuel wrote:
> I would like to configure the autovacuum in a way that it runs very frequ=
ently
> (i.e. after each update-statement). I tried the following settings on my =
table:
> alter table mytable set (autovacuum_vacuum_scale_factor=C2=A0 =3D 0.0);
> alter table mytable set (autovacuum_vacuum_cost_delay=C2=A0 =3D 0.0);
> alter table mytable set (autovacuum_vacuum_cost_limit=C2=A0 =3D 10000);
> alter table mytable set (autovacuum_vacuum_threshold=C2=A0 =3D 1);
> =C2=A0
> I do a lot of updates on a single tuple and I would expect that the autov=
acuum
> would start basically after each update (due to autovacuum_vacuum_thresho=
ld=3D1).
> But the autovacuum is not running.
> =C2=A0
> Is it possible to configure postgres to autovacuum very aggressively
> (i.e. after each update-statement)?

The formula in the source code is

        /* Determine if this table needs vacuum or analyze. */
        *dovacuum =3D force_vacuum || (vactuples > vacthresh) ||
            (vac_ins_base_thresh >=3D 0 && instuples > vacinsthresh);

So you need to update at least two rows to exceed the threshold.

If you want a single update to trigger autovacuum, you have to set
"autovacuum_vacuum_threshold" to 0.

I cannot imagine a situation where such a setting would be beneficial.
Particularly if you have lots of updates, this will just burn server resour=
ces
and may starve out other tables that need VACUUM.

Yours,
Laurenz Albe