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Re: Adding REPACK [concurrently]

Matthias van de Meent <boekewurm+postgres@gmail.com>

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From: Matthias van de Meent <boekewurm+postgres@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Antonin Houska <ah@cybertec.at>, Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-03-16T14:21:18Z
Lists: pgsql-hackers 
On Mon, 16 Mar 2026 at 13:21, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2026-Mar-16, Antonin Houska wrote:
>
> > One more problem related to the replication slot is that, due to the call of
> > CheckSlotPermissions() in setup_logical_decoding(), REPLICATION privilege is
> > required for REPACK (CONCURRENTLY) to run. That's not too user-friendly.
> >
> > I think the reason to require the REPLICATION privilege is that, in generic
> > case, the output plugin can access data of any table in the database. However
> > REPACK uses one particular plugin and that plugin only decodes changes of one
> > particular table. Thus I think we don't really need to call
> > CheckSlotPermissions(). Do I seem to miss something?
>
> Yeah, I don't think it makes sense to require REPLICATION privilege to
> run REPACK.

I don't think it makes sense to allow just any table owner to modify
the effective_wal_level GUC; which is what the effect would be of
removing the REPLICATION requirement from roles that want to REPACK
CONCURRENTLY -- and in doing so create logical slots, which increase
effective_wal_level to logical.

Creating a replication slot requires REPLICATION privilege, because it
consumes a (possibly very) limited server resource that can't be
increased without restart and because it impacts other backends' WAL
performance through effective_wal_level. Allowing users to consume
said resource without first having the appropriate permissions makes
this flag practically meaningless.

Note that most of my argument hinges on the impact on other, unrelated
databases/tables/sessions. Replication slots have a hard cap defined
at startup, and effective_wal_level increases the WAL generated by
practically all backends. If replication slot counts were SIGHUP, and
RelationIsLogicallyLogged() returned true only in databases with LR
slots, and only for the tables actually present in publications, I'd
consider this much less problematic. However, we don't live in that
world, so I am opposed to allowing table owners without REPLICATION to
take any/all replication slots.

Matthias van de Meent
Databricks (https://www.databricks.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