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Re: Adding REPACK [concurrently]

Antonin Houska <ah@cybertec.at>

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From: Antonin Houska <ah@cybertec.at>
To: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
Cc: alvherre@alvh.no-ip.org, Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-03-23T12:00:34Z
Lists: pgsql-hackers

Attachments

Antonin Houska <ah@cybertec.at> wrote:

> Antonin Houska <ah@cybertec.at> wrote:
> 
> > Antonin Houska <ah@cybertec.at> wrote:
> > 
> > > Srinath Reddy Sadipiralla <srinath2133@gmail.com> wrote:
> > > 
> > > > The concurrency test failed once. I tried to reproduce the below scenario
> > > > but no luck,i think the reason the assert failure happened because
> > > > after speculative insert there might be no spec CONFIRM or ABORT, thoughts?
> > > 
> > > Perhaps, I'll try. I'm not sure the REPACK decoding worker does anthing
> > > special regarding decoding. If you happen to see the problem again, please try
> > > to preserve the related WAL segments - if this is a bug in PG executor,
> > > pg_waldump might reveal that.
> > 
> > I could not reproduce the failure, and have no idea how speculative insert can
> > stay w/o CONFIRM / ABORT record. The only problem I could imagine is that
> > change_useless_for_repack() filters out the CONFIRM / ABORT record
> > accidentally, but neither code review nor debugger proves that
> > theory. (Actually if this was the problem, the test failure probably wouldn't
> > be that rare.)
> 
> I confirm that I was able to reproduce the crash using debugger and your more
> recent diagnosis [1]. Indeed, filtering was the problem.
> 
> Unfortunately, I wasn't able to make the crash easily reproducible using
> isolation tester. The problem is that the logical decoding is performed by a
> background worker, and when the backend executing REPACK waits for the
> background worker, which in turn waits on an injection point, the isolation
> tester does not recognize that it's effectively the backend who is waiting on
> the injection point. Therefore the isolation tester does not proceed to the
> next step.

I could not resist digging in it deeper :-) Attached is a test that reproduces
the crash - it includes the isolation tester enhancement that I posted
separately [1]. It crashes reliably with v43 [2] if your fix v43-0005 is
omitted.

[1] https://www.postgresql.org/message-id/4703.1774250534%40localhost
[2] https://www.postgresql.org/message-id/202603191855.fzsgsnyzfvpt%40alvherre.pgsql

-- 
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