On Mon, Aug 8, 2022 at 8:14 AM Matthias van de Meent <boekewurm+postg...@gmail.com> wrote: > I do not have intimate knowledge of this code, but shouldn't we also > add some sefety guarantees like the following in these blocks? Right > now, we'll keep underestimating the table size even when we know that > the count is incorrect. > > if (scanned_tuples > old_rel_tuples) > return some_weighted_scanned_tuples;
Not sure what you mean -- we do something very much like that already. We take the existing tuple density, and assume that that hasn't changed for any unscanned pages -- that is used to build a total number of tuples for the unscanned pages. Then we add the number of live tuples/scanned_tuples that the vacuumlazy.c caller just encountered on scanned_pages. That's often where the final reltuples value comes from. -- Peter Geoghegan
