Horton
Menu

Re: Adding REPACK [concurrently]

Antonin Houska <ah@cybertec.at>

View thread
From: Antonin Houska <ah@cybertec.at>
To: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-03-31T18:22:33Z
Lists: pgsql-hackers 
Srinath Reddy Sadipiralla <srinath2133@gmail.com> wrote:

> On Thu, Mar 26, 2026 at 1:42 AM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> 
>  As for lock upgrade, I wonder if the best way to handle this isn't to
>  hack the deadlock detector so that it causes any *other* process to die,
>  if they detect that they would block on REPACK.  Arguably there's
>  nothing that you can do to a table while its undergoing REPACK
>  CONCURRENTLY; any alterations would have to wait until the repacking is
>  compelted.  We can implement that idea simply enough, as shown in this
>  crude prototype. 
> 
> After testing this, I observed that it solves the scenario where a query is waiting
> on REPACK. For example, if a DROP TABLE requests an AEL and queues
> behind REPACK's ShareUpdateExclusiveLock, the deadlock detector comes
> when REPACK tries to upgrade to AEL, killing the DROP to prevent the circular
> queue deadlock, But the case I originally mentioned [1] was the reverse: what
> happens if a transaction already holds a lock that conflicts with the upcoming
> AEL upgrade (e.g., an analytical SELECT or an idle-in-transaction holding an AccessShareLock),
> but isn't waiting on REPACK at all?
> 
> In this case, there's no circular wait. The deadlock detector never fires. REPACK
> simply queues behind the SELECT, eventually hits its lock_timeout, aborts and
> cleans up.

Why should the user set non-zero lock_timeout before running REPACK?

-- 
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