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Re: Adding REPACK [concurrently]

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Noah Misch <noah@leadboat.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, 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: 2026-04-07T01:58:19Z
Lists: pgsql-hackers 
Hi,

On 2026-04-06 18:10:56 -0700, Noah Misch wrote:
> On Mon, Apr 06, 2026 at 05:11:30PM -0400, Andres Freund wrote:
> >   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?
> 
> By running AssertCouldGetRelation() during every INSERT statement, this
> detects cases that would be unsafe when the target of the INSERT happens to be
> a system catalog.

I see.


> Little of our INSERT/UPDATE coverage targets a system catalog.

Sure. We do have plenty DML doing heap_insert/update however.


> Hence, the current position is better for detection.

What if we returned early in AssertBufferLocksPermitCatalogRead() if
InterruptHoldoffCount == 0?  That'd only fail if some code manually did a
RESUME_INTERRUPTS() to balance the one acquired as part of the content lock?


> I wonder if this got slower in v19.  In v14-v18, the assert's cost is
> proportional to the number of held lwlocks, often 0 or 1.  In v19, it's
> proportional to PrivateRefCountHash cardinality.

Yea, plausible.  It will only scan PrivateRefCountHash if
PrivateRefCountOverflowed overflowed, but it did overflow in the case I was
testing...

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