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From: Antonin Houska <ah@cybertec.at>
To: Alvaro Herrera <alvherre@kurilemu.de>
Cc: Chao Li <li.evan.chao@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: REPACK (CONCURRENTLY) fails when replica identity index is dropped
Date: Thu, 10 Sep 2026 20:09:56 +0200
Message-ID: <45513.1789063796@localhost> (raw)
In-Reply-To: <aqKC6K_QO0OEv3gy@alvherre.pgsql>
References: <aqKC6K_QO0OEv3gy@alvherre.pgsql>

Alvaro Herrera <alvherre@kurilemu.de> wrote:

> On 2026-Sep-01, Alvaro Herrera wrote:
> 
> > On 2026-Sep-01, Antonin Houska wrote:
> > 
> > > I agree that the core issue is that we allow dropping an index that is being
> > > used as replica identity.
> > >
> > > Regarding catalog entries already broken this way, it appears that pg_upgrade
> > > fixes them because pg_dump does not issue "ALTER TABLE ... REPLICA IDENTITY
> > > USING INDEX ..." if there is not identity index. Thus after pg_restore,
> > > pg_class(relreplident) becomes REPLICA_IDENTITY_DEFAULT.
> > 
> > I agree that disallowing the drop is a sensible thing to do.
> 
> Actually, wouldn't it make more sense to reset the replica identity back
> to 'd' when the index is dropped, as in the attached patch?

Even though users probably do not drop the identity index too often, I think
it's possible that someone tries to drop an index that seems to be
unnecessary, but forgets that it's in use by logical replication. In such
case, I tend to consider ERROR better response than broken replication.

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

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