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Re: Adding REPACK [concurrently]

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Antonin Houska <ah@cybertec.at>
Cc: Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, 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: 2026-04-15T14:59:51Z
Lists: pgsql-hackers 
Hi,

On 2026-04-15 16:50:11 +0200, Antonin Houska wrote:
> I thought of a "hypothetical graph", which would include the to-be-granted
> lock, but the major issue is that it will not work correctly without the
> locking the LMGR's LW locks we do in CheckDeadLock():
> 
>     for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
>         LWLockAcquire(LockHashPartitionLockByIndex(i), LW_EXCLUSIVE);
> 
> And obviously, doing this each time we want to insert a lock into the queue
> would be bad for performance.

Hence my suggestion to do this as part of the deadlock check. Then we don't do
this unnecessary work outside of the case where we actually need it.

That does need to deal with the case of the deadlock check running first in
the backend doing repack, but that's not that hard - I think it'd be good
enough to set its deadlock timeout temporarily to a higher value. The backend
*should* still run the deadlock detector, because it could probably still get
into a deadlock (e.g. due to a pg_class access or something).

Greetings,

Andres Freund

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