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Re: Adding REPACK [concurrently]

Antonin Houska <ah@cybertec.at>

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From: Antonin Houska <ah@cybertec.at>
To: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-01-20T15:39:10Z
Lists: pgsql-hackers 
Mihail Nikalayeu <mihailnikalayeu@gmail.com> wrote:

> > if (size >= MaxAllocSize)
> Seems like we lost that check, I think it may be executed on storing
> the data

The tuple we process in store_change was created elsewhere (I think in
reorderbuffer.c), so I wouldn't re-check the size here.

> or before "tup = (HeapTuple) palloc(HEAPTUPLESIZE + t_len);"
> in apply_concurrent_changes

It's essentially the same length that we write in store_change() so I wouldn't
bother re-checking it here. In general, I doubt the constant is
appropriate. Its meaning is much more generic than the size of memory for a
tuple and even heap_form_tuple() does not use it.

> > bool done;
> I still think it is a confusing name.

I don't. The last call of process_concurrent_changes() tells the worker "Give
me the the next batch and we are done". Your proposal "exit_after_lsn_upto"
seems to me too verbose: the worker itself is supposed to know that it has to
reach the LSN passed via another argument.

> > chgdst.file_seq = WORKER_FILE_SNAPSHOT + 1;
> I think it is better to increment it once a snapshot is received.

The 'chgdst' is only defined in rebuild_relation_finish_concurrent(), no need
to use it where the snapshot is received (in rebuild_relation()).

> And rename to last_processed/last_improrted to be aligned with
> last_exported.

While DecodingWorkerShared deals with multiple files (not all of them
necessarily available for "consumer") and therefore it makes sense to
distinguish if file is exported or not, each instance of ChangeDest is
assigned particular file and the functions using it do not care if the file is
the last in the sequence or not.

Other proposals accepted, will be reflected in the next version.

-- 
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