Feedback-ID: id4a34324:Fastmail
Date: Mon, 6 Apr 2026 21:58:19 -0400
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>
Subject: Re: Adding REPACK [concurrently]
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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