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Re: Adding REPACK [concurrently]

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>, Noah Misch <noah@leadboat.com>
Cc: vignesh C <vignesh21@gmail.com>, 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: 2026-04-06T21:11:30Z
Lists: pgsql-hackers 
Hi,

I just saw this got committed and wanted to briefly play with it.  It works
nicely!


Except that at first I tried this in a debugging build, and was briefly rather
dismayed by the performance.  It was really slow.  But it's not really related
to repack / the patches here.


Turns out that it is to a good part due to
  heap_insert()
  ->CacheInvalidateHeapTuple()
  ->CacheInvalidateHeapTupleCommon()
  ->AssertCouldGetRelation()
not being cheap and running a *lot*.

Admittedly it's way worse if you build with -O0, which I tend to do to make
debugging easier.

In that config, the assert single-handled increases the time for a repack by
35% or so.


Noah, is there any reason we need to do the AssertCouldGetRelation() before
the !IsCatalogRelation(relation)? Given that the goal is to make
RelationGetRelid() safe, it doesn't seem there is?



It's totally valid to not have done so initially, this is a quite complicated
feature:

I saw this is using individual heap_insert()s during the
heapam_relation_copy_for_cluster().  Doing individual WAL logged inserts isn't
exactly cheap or efficient from a WAL volume perspective...

Is there anything other than round tuits preventing us from using
multi_insert?

That actually would also reduce the cost in the REPACK decoding worker, due to
having to parse far fewer WAL records.


Greetings,

Andres Freund

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