Date: Wed, 21 Jan 2026 09:47:20 -0800
From: Noah Misch <noah@leadboat.com>
To: Mark Dilger <mark.dilger@enterprisedb.com>
Cc: Nitin Motiani <nitinmotiani@google.com>,
	Andres Freund <andres@anarazel.de>, pgsql-hackers@postgresql.org
Subject: Re: Inval reliability, especially for inplace updates
Message-ID: <20260121174720.71.noahmisch@microsoft.com>
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On Wed, Jan 21, 2026 at 08:59:51AM -0800, Mark Dilger wrote:
> On Wed, Oct 23, 2024 at 7:54 PM Noah Misch <noah@leadboat.com> wrote:
> > I'm attaching the branch-specific patches for that and for the main fix.
> > Other notes from back-patching:
> >
> > - All branches change the ABI of PrepareToInvalidateCacheTuple(), a
> > function
> >   catcache.c exports for the benefit of inval.c.  No PGXN extension calls
> >   that, and I can't think of a use case in extensions.
> 
> Unfortunately, I can think of four.

Those are non-PGXN extensions, right?

Based on your experience, I probably should encourage packagers to do an early
check of the packages they build, especially if they build tableam modules not
found in PGXN.  How do you see it?

> I have four Table Access Methods that
> I now need to fork to be compatible with 18.0 and 18.1 on the one hand, and
> 18.2 onward on the other.

For what it's worth, the ABI break you quoted is the v14-v17 break, not the
v18 break:

- v18.2 (06b030e) is changing the CacheInvalidateHeapTupleInplace() ABI
- v14-v17 (e.g. 2e58802) is changing the PrepareToInvalidateCacheTuple() ABI

> I'm sorry I didn't follow this thread before it got pushed.
> 
> Is there a reason for doing this change in back branches?  The thread is
> pretty long, and I'm struggling to find a security or stability
> justification for the ABI break, but perhaps there is one.

Chiefly, the fix prevents data loss that arose via losing a relhasindex,
relfrozenxid, or datfrozenxid update.  (The log message of 0f69bed says
"another backend's DDL could then update the row without incorporating the
inplace update".)  For an example, see where that commit edits
src/test/isolation/expected/inplace-inval.out.