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Re: Adding REPACK [concurrently]

Antonin Houska <ah@cybertec.at>

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From: Antonin Houska <ah@cybertec.at>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Srinath Reddy Sadipiralla <srinath2133@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, 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: 2026-04-04T08:50:14Z
Lists: pgsql-hackers 
Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:

> On 2026-Apr-03, Antonin Houska wrote:
> 
> > diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
> > index 00b21ede481..c25dbeadff3 100644
> > --- a/src/backend/commands/repack_worker.c
> > +++ b/src/backend/commands/repack_worker.c
> 
> > @@ -233,6 +234,13 @@ repack_setup_logical_decoding(Oid relid)
> >  
> >  	EnsureLogicalDecodingEnabled();
> >  
> > +	/*
> > +	 * By declaring that our output plugin does not need shared catalogs, we
> > +	 * avoid waiting for completion of transactions running in other databases
> > +	 * than the one we're connected to.
> > +	 */
> > +	accessSharedCatalogsInDecoding = false;
> > +
> >  	/*
> >  	 * Neither prepare_write nor do_write callback nor update_progress is
> >  	 * useful for us.
> 
> I find this reliance on a global variable for this a bit icky.  Would it
> work to instead change the CreateInitDecodingContext() signature, so
> that instead of "bool need_full_snapshot" it has a three-valued boolean
> to distinguish the two cases from the original plus this new one?  I
> think the value could be stored in LogicalDecodingContext, from where
> standby_decode() could obtain it.

I agree that the global variable is not handy, but instead of modifying
CreateInitDecodingContext(), how about adding a boolean returning callback to
OutputPluginCallbacks? The point is that whether shared catalogs are needed
during the decoding or not is actually property of the plugin.

-- 
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