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From: Andres Freund <[email protected]>
To: Noah Misch <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: vignesh C <[email protected]>
Cc: Antonin Houska <[email protected]>
Cc: Srinath Reddy Sadipiralla <[email protected]>
Cc: Amit Kapila <[email protected]>
Cc: Mihail Nikalayeu <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: Pg Hackers <[email protected]>
Cc: Robert Treat <[email protected]>
Subject: Re: Adding REPACK [concurrently]
Date: Mon, 6 Apr 2026 21:58:19 -0400
Message-ID: <jaxapcek2yxbpyegajeim4aczdkjo4od7xxmtauf4fqtjtcpph@ws4anpqvjero> (raw)
In-Reply-To: <[email protected]>
References: <CALDaNm3tiKhtegx5Cawi34UjbHmNGEDNAtScGM1RgWRtV-5_0Q@mail.gmail.com>
	<[email protected]>
	<pbqm52nsviwojptiszg2g6pqntbhnhaotbxshiysnensshnuv5@v6pmney4jror>
	<[email protected]>

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

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