From: Antonin Houska <ah@cybertec.at>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
cc: Robert Treat <rob@xzilla.net>,
    Pg Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Adding REPACK [concurrently]
In-reply-to: <202508191222.ghumvyzw4cmj@alvherre.pgsql>
References: <202508191222.ghumvyzw4cmj@alvherre.pgsql>
Comments: In-reply-to Alvaro Herrera <alvherre@alvh.no-ip.org>
   message dated "Tue, 19 Aug 2025 14:22:47 +0200."
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Date: Wed, 20 Aug 2025 10:33:49 +0200
Message-ID: <18831.1755678829@localhost>
Archived-At: 
 <https://www.postgresql.org/message-id/18831.1755678829%40localhost>
Precedence: bulk

Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:

> On 2025-Aug-16, Robert Treat wrote:
>=20
> > On Tue, Aug 5, 2025 at 4:59=E2=80=AFAM Antonin Houska <ah@cybertec.at> =
wrote:
>=20
> > > Now that we want to cover the CLUSTER/VACUUM FULL completely, I've ch=
ecked the
> > > options of VACUUM FULL. I found two items not supported by REPACK (bu=
t also
> > > not supported by by CLUSTER): ANALYZE and SKIP_DATABASE_STATS. Maybe =
just
> > > let's mention that in the user documentation of REPACK?
> >=20
> > I would note that both pg_repack and pg_squeeze analyze by default,
> > and running "vacuum full analyze" is the recommended behavior, so not
> > having analyze included is a step backwards.
>=20
> Make sense to add ANALYZE as an option to repack, yeah.
>=20
> So if I repack a single table with
>   REPACK (ANALYZE) table USING INDEX;
>=20
> then do you expect that this would first cluster the table under
> AccessExclusiveLock, then release the lock to do the analyze step, or
> would the analyze be done under the same lock?  This is significant for
> a query that starts while repack is running, because if we release the
> AEL then the query is planned when there are no stats for the table,
> which might be bad.
>=20
> I think the time to run the analyze step should be considerable shorter
> than the time to run the repacking step, so running both together under
> the same lock should be okay.

AFAICS, VACUUM FULL first releases the AEL, then it analyzes the table. If
users did not complain so far, I'd assume that vacuum_rel() (effectively
cluster_rel() in the FULL case) does not change the stats that much.

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