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Re: Adding REPACK [concurrently]

Mihail Nikalayeu <mihailnikalayeu@gmail.com>

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From: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
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>
Date: 2026-04-30T11:24:41Z
Lists: pgsql-hackers 
Hello!

On Mon, Apr 27, 2026 at 6:25 AM Amit Kapila <amit.kapila16@gmail.com> 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)=(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 = 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=stress (as done in [1]).

[0]: https://www.postgresql.org/message-id/flat/CADzfLwUitd5J17O9FUxNGrZBurOpL6n%2BtnS6dgArXi-i9DNxhg%40mail.gmail.com#c5945a539400676cdfd72eec6c101710
[1]: https://www.postgresql.org/message-id/flat/CAHg%2BQDcQak4jx_6X2_Ws98rzG%3DxBARLjqm_%3D56wTRUtNsY4DZQ%40mail.gmail.com
[2]: https://www.postgresql.org/message-id/flat/CADzfLwWC%2BKxYWb-2QotWaz-q1LK8koLNVUR1Q8obAtt%2BR_sORA%40mail.gmail.com#c8435a284f8893bbc1a891c56be5e158

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Allow old WAL recycling during REPACK CONCURRENTLY

  2. Advance restart_lsn more eagerly in LogicalConfirmReceivedLocation

  3. Remove unnecessary signal handler change

  4. Improve REPACK (CONCURRENTLY) error messages some more

  5. Revert "Allow logical replication snapshots to be database-specific"

  6. Move REPACK (CONCURRENTLY) test out of stock regression tests

  7. REPACK: do not require REPLICATION or LOGIN

  8. Add missing initialization

  9. Simplify declaration of memcpy target

  10. Reserve replication slots specifically for REPACK

  11. doc: Add an example of REPACK (CONCURRENTLY)

  12. Allow logical replication snapshots to be database-specific

  13. Avoid different-size pointer-to-integer cast

  14. Fix valgrind failure

  15. Add CONCURRENTLY option to REPACK

  16. Rename cluster.c to repack.c (and corresponding .h)

  17. Allow index_create to suppress index_build progress reporting

  18. Make index_concurrently_create_copy more general

  19. Document the 'command' column of pg_stat_progress_repack

  20. Introduce the REPACK command

  21. Toggle logical decoding dynamically based on logical slot presence.

  22. Split vacuumdb to create vacuuming.c/h

  23. Remove ReorderBufferTupleBuf structure.

  24. Revert changes to CONCURRENTLY that "sped up" Xmin advance

  25. VACUUM: ignore indexing operations with CONCURRENTLY