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Re: Adding REPACK [concurrently]

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Antonin Houska <ah@cybertec.at>
Cc: Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-02-25T16:25:54Z
Lists: pgsql-hackers 
On 2026-Feb-25, Antonin Houska wrote:

> > Hmm, so on the apply side when reading the file, we would first reach
> > each toast attribute value, which we know to insert directly to the
> > toast table (keeping track of each individually toast pointer as we do
> > so); then we reach the heap tuple itself, we [... somehow ...] interpret
> > these external indirect toast pointers and substitute the toast pointers
> > that we created.  So we never have to construct the entire tuple, or
> > indeed do anything else with the toasted values other than insert them
> > into the toast table.
> 
> Yes, that's what I mean.

Makes sense.  Would you be able to try and implement that?

> The problem I see here is that for UPDATE you need the old tuple to determine
> if its TOAST value should be deleted or if the new tuple should reuse it -
> this is how I understand toast_tuple_init(). So the worker would have to store
> all the changes somewhere temporarily until it can fully apply the changes
> (i.e. until the initial copy and index build is complete).

Ah, you're right, that won't work.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
Tom: There seems to be something broken here.
Teodor: I'm in sackcloth and ashes...  Fixed.
                               http://postgr.es/m/482D1632.8010507@sigaev.ru

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