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From: Masahiko Sawada <sawada.mshk@gmail.com>
Date: Fri, 8 May 2026 16:22:15 -0700
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 <CAD21AoC=kWLBPYFOOp-t_G7s1t0hOhuwMiKApyESDKt6HHQAQQ@mail.gmail.com>
Subject: Re: Adding REPACK [concurrently]
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Antonin Houska <ah@cybertec.at>,
	Mihail Nikalayeu <mihailnikalayeu@gmail.com>,
 Andres Freund <andres@anarazel.de>,
	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>
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On Fri, May 8, 2026 at 6:58=E2=80=AFAM Alvaro Herrera <alvherre@alvh.no-ip.=
org> wrote:
>
> On 2026-May-08, Amit Kapila wrote:
>
> > On Wed, May 6, 2026 at 1:55=E2=80=AFPM Antonin Houska <ah@cybertec.at> =
wrote:
>
> > Some issues/inefficiencies regarding this fix and base code related to
> > db-specific snapshots built during decoding: [...]
>
> Thanks for spending time reviewing this code.  I think none of these
> problems are fundamental in nature, but they are obviously worth
> addressing for 19.  If we hit some roadblock, we can still revert only
> db-specific snapshots.
>

I'm still studying REPACK (CONCURRENTLY), and I have a question about
db-specific decoder; as far as I read the codes, any decoding plugin
can use db-specific decoder by setting need_shared_catalog=3Dfalse but
should we prevent such slots from being created on standbys? I'm a bit
concerned that plugin developers inadvertently set
need_shared_catalog=3Dfalse in the startup callback and users would
create such slots on standbys.  For instance, if we create a logical
slot with pgrepack plugin on the standby, we would get an assertion
failure as the db-specific decoder tries to call LogStandbySnapshot()
via SnapBuildProcessRunningXacts(). Even if we add
!RecoveryInProgress() check there, the db-specific decoder on standbys
requires for the primary server to run a REPACK (CONCURRENTLY).

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com