Re: pgsql: Avoid improbable PANIC during heap_update.

Peter Geoghegan <pg@bowt.ie> writes:
> On Fri, Sep 30, 2022 at 2:28 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Ugh ... I think I see the problem.  There's still one path through
>> RelationGetBufferForTuple that fails to guarantee that it's acquired
>> a vmbuffer pin if the all-visible flag becomes set in the otherBuffer.

> FWIW it seems possible that the Postgres 15 vacuumlazy.c work that
> added lazy_scan_noprune() made this scenario more likely in practice
> -- even compared to Postgres 14.

Could be, because we haven't seen field reports of this in v14 yet.
And there's still no hard evidence of a bug pre-14.  Nonetheless,
I'm inclined to backpatch to v12 as 34f581c39 was.

            regards, tom lane