Re: Assert in heapgettup_pagemode() fails due to underlying buffer change

On Fri, Jun 7, 2024 at 3:06 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> On Fri, Jun 7, 2024 at 3:00 PM Alexander Lakhin <exclusion@gmail.com> wrote:
> > My bisect run ended with:
> > 210622c60e1a9db2e2730140b8106ab57d259d15 is the first bad commit
> >
> > Author: Thomas Munro <tmunro@postgresql.org>
> > Date:   Wed Apr 3 00:03:08 2024 +1300
> >
> >      Provide vectored variant of ReadBuffer().
> >
> > Other buildfarm failures with this Assert I could find kind of confirm this:
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=calliphoridae&dt=2024-04-03%2003%3A32%3A18
> > (presumably a first failure of this sort)
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tamandua&dt=2024-04-04%2015%3A38%3A16
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=margay&dt=2024-05-07%2004%3A00%3A08
>
> Looking...

What Noah described[1] is what should be happening already, I think,
but 210622c6 unconditionally zeroed the page.  Oops.  The attached
seems to cure his repro for me.  Does it also cure your test?  I
couldn't see that variant myself for some reason, but it seems to make
sense as the explanation.  I would probably adjust the function name
or perhaps consider refactoring slightly, but first let's confirm that
this is the same issue and fix.

[1] https://www.postgresql.org/message-id/flat/20240512171658.7e.nmisch@google.com