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Re: Adding REPACK [concurrently]

Mihail Nikalayeu <mihailnikalayeu@gmail.com>

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From: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
To: Antonin Houska <ah@cybertec.at>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-01-15T17:05:02Z
Lists: pgsql-hackers 
Hello!

Antonin Houska <ah@cybertec.at>:

As the test runs pgbench with --client=30 and the default value of
max_worker_processes is 8, I'm not sure this is a leak. I've increased this
parameter I couldn't see the error anymore.


Hm, as far as I remember only single repack may be executed in test
(because of locking on test itself and also REPACK).

At least still feel suspicious.


I agree that this is due to the missing MVCC safety feature. I commented
that
check in the script for now.


I don't think so. In case of non-MVCC safety we should see 0 or correct
sum. But script failed with 490588...

But should see 500500 (if I correctly calculated sum of numbers from 1 to
1000)...

Besides that, I saw some deadlocks. I think this was due to the fact that
multiple rows are updated per transaction, and that the keys are random, so
it
can happen that two transactions try to update the same rows in different
order. I increased the number of rows in the test table to 10000 and don't
see
the deadlocks anymore.


I think better to use min/max in updates to be sure (update lower id first).

This is tricky. I could reproduce the problem on my FreeBSD box a few times,
never on Linux (no idea if the OS makes the difference since HW is also
quite
different, but CI also seemed to fail more often on FreeBSD.)


You may try to play with no_hot parameter in test - maybe it will provide
some clue.

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