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From: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Date: Thu, 30 Apr 2026 13:24:41 +0200
Message-ID: 
 <CADzfLwWnbKcb3v8sStdgNE=WNc3uUqx5SiS4zftX2UaEfNzG5w@mail.gmail.com>
Subject: Re: Adding REPACK [concurrently]
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Antonin Houska <ah@cybertec.at>,
	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>
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Hello!

On Mon, Apr 27, 2026 at 6:25=E2=80=AFAM Amit Kapila <amit.kapila16@gmail.co=
m> wrote:
> Alvaro, others, what is your take on this?

I agree with you here - we should AT LEAST make that an ERROR instead
of an assert and also check it during cache access (not only during
the scan because of cache misses).
But I think it will still be fragile in case of some extensions installed.

Anyway... We also have an issue with correctness right now.

I took the old stress test from [0] (the first two) and it fails now,
even with the fix from [1] ("Possible premature SNAPBUILD_CONSISTENT
with DB-specific running_xacts").

It looks like [1] fixes 008_repack_concurrently.pl, but
007_repack_concurrently.pl fails anyway, including

     pgbench: error: client 1 script 0 aborted in command 10 query 0:
ERROR:  could not create unique index "tbl_pkey_repacknew"
     # DETAIL:  Key (i)=3D(383) is duplicated.
and
     'pgbench: error: pgbench:client 23 script 0 aborted in command 31
query 0: ERROR:  division by zero

Last one is not MVCC-related; you can see from the logs that it
performs something like SELECT (509063) / 0 when the table sum
changes.

Setting need_shared_catalogs =3D true make them pass, so something is
wrong with its correctness.

P.S.
I think it is good idea to add these stress tests to the source tree,
perhaps with some kind PG_TEST_EXTRA=3Dstress (as done in [1]).

[0]: https://www.postgresql.org/message-id/flat/CADzfLwUitd5J17O9FUxNGrZBur=
OpL6n%2BtnS6dgArXi-i9DNxhg%40mail.gmail.com#c5945a539400676cdfd72eec6c10171=
0
[1]: https://www.postgresql.org/message-id/flat/CAHg%2BQDcQak4jx_6X2_Ws98rz=
G%3DxBARLjqm_%3D56wTRUtNsY4DZQ%40mail.gmail.com
[2]: https://www.postgresql.org/message-id/flat/CADzfLwWC%2BKxYWb-2QotWaz-q=
1LK8koLNVUR1Q8obAtt%2BR_sORA%40mail.gmail.com#c8435a284f8893bbc1a891c56be5e=
158