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Re: Adding REPACK [concurrently]

vignesh C <vignesh21@gmail.com>

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From: vignesh C <vignesh21@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Antonin Houska <ah@cybertec.at>, 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: 2026-04-06T10:01:27Z
Lists: pgsql-hackers 
On Mon, 6 Apr 2026 at 15:08, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2026-Apr-06, vignesh C wrote:
>
> > On Mon, 6 Apr 2026 at 02:12, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> > Few comments:
>
> Thanks for reviewing this patch!
>
> > 1) Can we add a comment why we should error out here, as repack
> > concurrently requires this whereas repack does not require this check.
> > Even if it is required for decoding can't it be handled by replica
> > identity full:
> > +       /*
> > +        * If the identity index is not set due to replica identity being, PK
> > +        * might exist.
> > +        */
> > +       ident_idx = RelationGetReplicaIndex(rel);
> > +       if (!OidIsValid(ident_idx) && OidIsValid(rel->rd_pkindex))
> > +               ident_idx = rel->rd_pkindex;
> > +       if (!OidIsValid(ident_idx))
> > +               ereport(ERROR,
> > +
> > errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
> > +                               errmsg("cannot process relation \"%s\"",
> > +                                          RelationGetRelationName(rel)),
> > +                               errhint("Relation \"%s\" has no
> > identity index.",
> > +                                               RelationGetRelationName(rel)));
>
> Ah, I was just rewriting that comment moments ago.  I think we could
> make it work with replica identity full in theory, but I'm guessing it
> would be useless.  You really need an index that lets you locate the
> affected tuples; otherwise the replay would take forever.  If the table
> is big, that would make the whole thing unworkable.  If the table isn't
> big, then you can probably just use straight repack without too much
> disruption.
>
>         /*
>          * Obtain the replica identity index -- either one that has been set
>          * explicitly, or the primary key.  If none of these cases apply, the
>          * table cannot be repacked concurrently.  It might be possible to have
>          * repack work with a FULL replica identity; however that requires more
>          * work and is not implemented yet.
>          */

Should this be mentioned in XXX comment:
It might be possible to have repack work with a FULL replica identity;
however that requires more work and is not implemented yet.

> > 2) Do you think it will be good to add a test to simulate a case where
> > one of the swap_replation_files is successful and a failure after
> > that. We can verify that the oid should still point to old oids:
>
> Hmm, it's not clear to me in which cases this can happen.  Are you
> thinking that the first swap_replation_files call dies because of
> out-of-memory?

Yes, I was thinking of that.

> Note that the really weird cases, like pg_class or mapped relations, are
> directly rejected.  So we don't get into the branch with
> !RelFileNumberIsValid, and so on.
>
> I mean -- I'm not opposed to adding a test case for it.  But I suspect
> it's going to be somewhat annoying to write.

I will verify this scenario through debugger.

Regards,
Vignesh

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