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Re: Adding REPACK [concurrently]

Mihail Nikalayeu <mihailnikalayeu@gmail.com>

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From: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
To: Andres Freund <andres@anarazel.de>
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: 2026-04-08T23:36:00Z
Lists: pgsql-hackers 
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.
DML actions are ok for us; REPACK will wait for them while getting
AEL. Later changes will be applied by REPACK backend while holding
AEL.

One more thing we may prevent from sneaking into that hole is a
VACUUM. It will not break anything, but will be huge waste of time and
resources.

> And you need to wait for all pre-existing locks to have been released.  That
> doesn't really get easier by what you propose.

 Do you mean locks from other sessions accessing the table? Is it done
automatically while waiting for AEL?

> 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.

> And even if that were not the case, there are
> several paths to locking relations that don't ever go anywhere near
> CheckTableNotInUse().

But those aren't DDL, so they shouldn't be the problem (CREATE TRIGGER
might be - it seems to ignore CheckTableNotInUse, but perhaps it's
fine).

So, in my undeerstanding Amit's idea has two parts: "set flag and
release/re-acquire" + "use CheckTableNotInUse (or some place like
that) to check the flag and fail for DDL commands."

Reading your arguments again, they all seem valid under the assumption
that we still hold SUEL while requesting AEL.
I suspect you may have just skimmed past the 'release/re-acquire' part
- but more probably I missed something.

Best regards,
Mikhail.

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