Re: BUG #17257: (auto)vacuum hangs within lazy_scan_prune() - Mailing list pgsql-bugs

On Fri, Apr 26, 2024 at 4:46 PM Melanie Plageman
<melanieplageman@gmail.com> wrote:
> I have a more basic question. How could GlobalVisState->maybe_needed
> going backwards cause a problem with relfrozenxid? Yes, if
> maybe_needed goes backwards, we may not remove a tuple whose xmin/xmax
> are older than VacuumCutoffs->OldestXmin. But, if that tuple's
> xmin/xmax are older than OldestXmin, then wouldn't we freeze it?

You can't freeze every XID older than OldestXmin.
heap_prepare_freeze_tuple() isn't prepared for HEAPTUPLE_DEAD tuples,
and expects that those will be taken care of by the time it is called.

--
Peter Geoghegan