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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: 2026-04-01T12:21:40Z
Lists: pgsql-hackers 
On Wed, Apr 1, 2026 at 5:08 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2026-Apr-01, Amit Kapila wrote:
>
> > 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.
>
> If we just let REPACK finish, it will also renew the table's XID, so
> autovacuum is not needed in that case.  I mean, there's no reason to let
> autovacuum process the contents of a table that is going to be replaced
> completely.
>
> One potentially problematic case would be that an emergency autovacuum
> has been running for a long time and about to finish, and REPACK is
> started.  But in that case, autovacuum already has ShareUpdateExclusive,
> so REPACK wouldn't be able to start at all, which means it won't kill
> autovacuum.  And in the case where autovacuum is doing emergency
> vacuuming, then it won't commit suicide, so it will be able to complete
> before repack starts.
>
> > 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?
>
> I don't understand exactly which scenario you're concerned about.  Is
> there a long-running query which, after spending a lot of time running a
> report, tries to upgrade its lock level on the table?  Keep in mind that
> this check only runs when the affected session runs the deadlock
> checker, which means it's been waiting to acquire a lock for
> deadlock_timeout seconds.  It's not repack that kills the query.
>
> [ ... reflects ...]  Oh, actually what Srinath proposed does exactly
> that -- kill other queries.  Hmm, yeah, I'm less sure about that
> particular bit.
>

Yes, I was talking about Srinath's proposed solution. Do we need to do
anything about 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