Re: Adding REPACK [concurrently]

Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:

> On 2026-Apr-20, Antonin Houska wrote:
>
> > Antonin Houska <ah(at)cybertec(dot)at> wrote:
> >
> > > It was discussed earlier [1] and the concerns about possibly excessive
> > > resource consumptions were addressed by [2]. So I think it the fix was 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 checkpoint),
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: =?UTF-8?q?=C3=81lvaro=20Herrera?= <alvherre(at)kurilemu(dot)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=replica.

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

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