Horton
Menu

Re: Adding REPACK [concurrently]

Andres Freund <andres@anarazel.de>

View thread
From: Andres Freund <andres@anarazel.de>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Antonin Houska <ah@cybertec.at>, Srinath Reddy Sadipiralla <srinath2133@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-04-07T20:24:04Z
Lists: pgsql-hackers 
Hi,

On 2026-04-07 00:22:32 +0200, Alvaro Herrera wrote:
> From 4303eea0a72408183f9f5afcf8d2801df20f8ffe Mon Sep 17 00:00:00 2001
> From: Antonin Houska <ah@cybertec.at>
> Date: Wed, 1 Apr 2026 17:35:47 +0200
> Subject: [PATCH v56 3/3] Error out any process that would block at REPACK
> 
> Any process waiting on REPACK to release its lock would actually cause
> it to deadlock when it tries to upgrade its lock to AEL, losing all work
> done to that point.  We avoid this by teaching the deadlock detector to
> raise an error when this condition is detected.

I'm rather doubtful that that is ok. Won't this make it basically unsafe to
use repack in way way too many situations? If sessions start erroring out,
rather than wait, because they briefly lock a relation or such it'll imo make
this rather unsafe in production.

ISTM that the proper fix here might be to allow repack to do a lock upgrade
that jumps to the front of the lock's wait queue. The lock upgrade is the
reason for the deadlock, right? And the reason it will often cause a deadlock
is that the repack will be at the tail, rather than the front of the wait
queue. So let's fix that.

Jumping the queue won't make the lock upgrade immediately, of course, but I
think it would fix the issue of the repack, rather than some other process,
getting cancelled?

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