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From: Antonin Houska <[email protected]>
To: Alvaro Herrera <[email protected]>
Cc: Robert Treat <[email protected]>
Cc: Pg Hackers <[email protected]>
Subject: Re: Adding REPACK [concurrently]
Date: Wed, 20 Aug 2025 10:33:49 +0200
Message-ID: <18831.1755678829@localhost> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Alvaro Herrera <[email protected]> wrote:

> On 2025-Aug-16, Robert Treat wrote:
> 
> > On Tue, Aug 5, 2025 at 4:59 AM Antonin Houska <[email protected]> wrote:
> 
> > > Now that we want to cover the CLUSTER/VACUUM FULL completely, I've checked the
> > > options of VACUUM FULL. I found two items not supported by REPACK (but also
> > > not supported by by CLUSTER): ANALYZE and SKIP_DATABASE_STATS. Maybe just
> > > let's mention that in the user documentation of REPACK?
> > 
> > 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.
> 
> Make sense to add ANALYZE as an option to repack, yeah.
> 
> So if I repack a single table with
>   REPACK (ANALYZE) table USING INDEX;
> 
> 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.
> 
> 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.

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

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