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Re: Adding REPACK [concurrently]

Antonin Houska <ah@cybertec.at>

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From: Antonin Houska <ah@cybertec.at>
To: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-03-16T20:15:14Z
Lists: pgsql-hackers 
Matthias van de Meent <boekewurm+postgres@gmail.com> wrote:

> I agree it's not user-friendly, but that's the point of limiting
> permissions. Users can't install c-functions without SUPERUSER,
> because it can cause cluster instability and crashes. Users can't
> create slots without REPLICATION, because they'll be able to
> negatively impact the whole cluster's performance, and possibly,
> stability, when taking up replication slots that otherwise would be
> used for critical HA purposes.

I thought these attributes exist primarily for security purposes. If
non-SUPERUSER user could install C-functions, it'd be easy to install code
that leaks data. REPLICATION is currently the only way to limit access to the
the publisher's data as there is no ACL for publications.

And regarding resources, the REPLICATION attribute alone does not pose a limit
on resource consumption unless you limit the total number of sessions of all
the REPLICATION users at the same time.

Anyway (fortunately?), the concurrent use of slots by REPACK is limited
because, during the initialization of logical decoding, the backend needs to
wait for all the transactions having XID assigned to finish, and these include
the already running REPACK commands. See SnapBuildWaitSnapshot() and callers
if you're interested in details.

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

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