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Re: Adding REPACK [concurrently]

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Antonin Houska <ah@cybertec.at>, 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: 2026-04-09T14:13:26Z
Lists: pgsql-hackers 
Hi,

On 2026-04-09 01:36:00 +0200, Mihail Nikalayeu wrote:
> Hello, Andres!
> 
> On Wed, Apr 8, 2026 at 7:22 PM Andres Freund <andres@anarazel.de> wrote:
> > I don't think this is a viable path.  You need to prevent any further lock
> > acquisitions on the relation to be able to swap it, not just conflicting DDL.
> 
> AFAIU, Amit's main idea is that we currently upgrade the lock instead
> of **releasing and re-acquiring** it because we fear DDL between those
> actions.

I got that, I just don't think it's going to work in any sort of way
reasonably well.

The fix here should be to make the system understand how to make lock upgrades
as safe as possible, not to hack around the corners.  For that you need to
teach the deadlock detector about all of this properly.


> > I don't think CheckTableNotInUse() would work anyway - don't we already hold
> > locks by the point we call it?
> 
> Yes, the DDL session already holds locks by the time
> CheckTableNotInUse is called - but is that really the problem? They
> will be released on error.

There's no guarantee they get there if it's done after the lock
acquisition. It can be part of a more complicated lock cycle.

Greetings,

Andres Freund

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