From: Antonin Houska <ah@cybertec.at>
To: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
cc: Amit Kapila <amit.kapila16@gmail.com>,
    Andres Freund <andres@anarazel.de>,
    Alvaro Herrera <alvherre@alvh.no-ip.org>,
    Srinath Reddy Sadipiralla <srinath2133@gmail.com>,
    Matthias van de Meent <boekewurm+postgres@gmail.com>,
    Pg Hackers <pgsql-hackers@lists.postgresql.org>,
    Robert Treat <rob@xzilla.net>
Subject: Re: Adding REPACK [concurrently]
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Comments: In-reply-to Mihail Nikalayeu <mihailnikalayeu@gmail.com>
   message dated "Thu, 09 Apr 2026 11:11:16 +0200."
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Date: Thu, 09 Apr 2026 11:26:29 +0200
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Mihail Nikalayeu <mihailnikalayeu@gmail.com> wrote:

> On Thu, Apr 9, 2026 at 10:43=E2=80=AFAM Antonin Houska <ah@cybertec.at> w=
rote:
> > This approach LGTM when it comes to concurrent DDLs. However, consider =
REPACK
> > holding ShareUpdateExclusiveLock (SUEL) and VACUUM (w/o VACOPT_SKIP_LOC=
KED)
> > waiting for the same lock. Once REPACK releases its SUEL, VACUUM gets i=
t and
> > processes the table, then REPACK finally gets AccessExclusiveLock (AEL)=
 and
> > finishes too.
>=20
> > One more thing we may prevent from sneaking into that hole is a
> > VACUUM. It will not break anything, but will be huge waste of time and
> > resources.
>=20
>=20
> I thought about that too, I think we may just add some kind of
> CheckTableNotInUse in VACUUM after getting the SUEL.

Sure, it's possible, but IMO the principal question is whether REPACK should
let VACUUM and DDLs error out, or just let them wait.

--=20
Antonin Houska
Web: https://www.cybertec-postgresql.com