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Re: Adding REPACK [concurrently]

Mihail Nikalayeu <mihailnikalayeu@gmail.com>

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From: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
To: Antonin Houska <ah@cybertec.at>
Cc: Andres Freund <andres@anarazel.de>, Amit Kapila <amit.kapila16@gmail.com>, 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: 2026-04-16T11:18:55Z
Lists: pgsql-hackers 
Hello!

On Wed, Apr 15, 2026 at 8:28 PM Antonin Houska <ah@cybertec.at> wrote:
> just after step 4, the two session will probably up in a deadlock anyway. In
> other words, even if REPACK does the check early, it does not prevent other
> sessions from getting in the way.
>
> Maybe I'm still missing something.

I was trying to solve that by using another approach: the ability to
define a "future lock" [0]. It is declared even before taking the
actual lock, so, no race is possible.

That approach works correctly except one case -
ShareUpdateExclusiveLock from another backend, I described it here [1]
a little bit.

For now, I don't know how to solve it without a performance downgrade.

[0]: https://github.com/michail-nikolaev/postgres/commit/ba0f4247dad3d96b8282cd18056b7776cd69317c
[1]: https://www.postgresql.org/message-id/flat/CADzfLwU8Qw6LXFHO7Tbjc-O7o%2BtM26jdnOJBWqYLu61rf7bO%2Bg%40mail.gmail.com#1e96f8882363afb2fc53c2f08346f527

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