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Re: Adding REPACK [concurrently]

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Srinath Reddy Sadipiralla <srinath2133@gmail.com>, Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Antonin Houska <ah@cybertec.at>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-04-01T09:39:31Z
Lists: pgsql-hackers 
On Tue, Mar 31, 2026 at 11:54 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2026-Mar-31, Srinath Reddy Sadipiralla wrote:
>
> > In this case, there's no circular wait. The deadlock detector never
> > fires.  REPACK simply queues behind the SELECT, eventually hits its
> > lock_timeout, aborts and cleans up.Initially, I thought this cleanup
> > was expected behavior. But after seeing your solution to protect
> > REPACK from losing its transient table work, I thought it's "not
> > expected".
>
> Yeah.  Keep in mind that REPACK could have been running for many hours
> or even days before it reaches the point of acquiring its AEL lock to do
> the final swap; and it may well be critical work.  We do not want to
> lose it.  So whatever is waiting to obtain a lock on the table, or
> already has a lock on the table, has to yield.
>
> > If the goal is to prevent REPACK's work from being wasted, should we
> > error out the backend that is making REPACK wait during the final swap
> > phase? I am thinking of something conceptually similar to
> > ResolveRecoveryConflictWithLock, actively cancelling the conflicting
> > session to allow the AEL upgrade to proceed.
>
> Something like that might be appropriate, yeah.
>

What about if the blocking process is an autovacumm that is working to
prevent XID wraparound? I think we already avoid killing it in such
cases. BTW, one can say that cancelling a long-running report query
also wastes a lot of effort of the user generating such a report. Why
can't REPACK wait for such a select to finish instead of cancelling
it?

-- 
With Regards,
Amit Kapila.

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