From: Antonin Houska <ah@cybertec.at>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
cc: Justin Pryzby <pryzby@telsasoft.com>,
    Mihail Nikalayeu <mihailnikalayeu@gmail.com>,
    Andres Freund <andres@anarazel.de>,
    Amit Kapila <amit.kapila16@gmail.com>,
    Srinath Reddy Sadipiralla <srinath2133@gmail.com>,
    Matthias van de Meent <boekewurm+postgres@gmail.com>,
    pgsql-hackers@lists.postgresql.org, Robert Treat <rob@xzilla.net>
Subject: Re: Adding REPACK [concurrently]
In-reply-to: <aeYQwx9WwD-g-Fc9@alvherre.pgsql>
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Comments: In-reply-to Alvaro Herrera <alvherre@alvh.no-ip.org>
   message dated "Mon, 20 Apr 2026 13:45:35 +0200."
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Date: Mon, 20 Apr 2026 15:46:13 +0200
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Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:

> On 2026-Apr-20, Antonin Houska wrote:
> =

> > Antonin Houska <ah@cybertec.at> wrote:
> > =

> > > It was discussed earlier [1] and the concerns about possibly excessi=
ve
> > > resource consumptions were addressed by [2]. So I think it the fix w=
as just
> > > forgotten. Attached here.
> > =

> > Sorry, I attached wrong patch. This is what I meant.
> =

> Yeah, I had also written the same patch a couple of days ago.
> =

> BTW I ran into a small problem after adding some tests in cluster.sql
> that would exercise this -- that test would die more or less randomly
> but frequently in CI (which it never did in my laptop) because of the
> size of the snapshot,
> =

>  ALTER TABLE ptnowner1 REPLICA IDENTITY USING INDEX ptnowner1_i_key;
>  REPACK (CONCURRENTLY) ptnowner1;
> +ERROR:  initial slot snapshot too large
> +CONTEXT:  REPACK decoding worker
>  RESET SESSION AUTHORIZATION;
> =

> I think the solution for this is to move cluster to a separate parallel
> test.  The one where it is now is a bit too crowded.  Maybe the one for
> compression is okay?  I'll test and push if I see it passing CI.

That shouldn't break anything, but I have no idea why this problem was not
triggered (as far as I remember) by the stress tests we ran during
development.

I thought that it might be due to less frequent calls of
SnapBuildPurgeOlderTxn(), which might in turn be due to less frequent
checkpoints (because xl_running_xacts is typically written during checkpoi=
nt),
and that checkpoints may be deliberately less frequent to make regression
tests run faster. However I don't immediately see related configuration in=
 the
regression test setup.

> Another obvious thing after adding tests is that the LOGIN privilege is
> required, which is also quite bogus IMO.  0002 here should solve that.

ok

> >From b3d4158356f4914d2b0cba86eef6994c0ee50ab9 Mon Sep 17 00:00:00 2001
> From: =3D?UTF-8?q?=3DC3=3D81lvaro=3D20Herrera?=3D <alvherre@kurilemu.de>
> Date: Mon, 20 Apr 2026 11:38:48 +0200
> Subject: [PATCH 1/2] REPACK: do not require the user to have REPLICATION

> Because there are now successful concurrent repack runs in the
> regression tests, we're forced to run test_plan_advice under
> wal_level=3Dreplica.

Is this an attempt to disable REPACK (CONCURRENTLY)? That would require
wal_level=3Dminimal (due to commit 67c20979ce). In which way does REPACK s=
eem to
break test_plan_advice?

-- =

Antonin Houska
Web: https://www.cybertec-postgresql.com