On Wed, Jan 18, 2023 at 7:04 PM Andres Freund <andres@anarazel.de> wrote:
> > You seem to be saying that it's a problem if we don't update reltuples
> > -- an estimate -- when less than 2% of the table is scanned by VACUUM.
> > But why? Why can't we just do nothing sometimes? I mean in general,
> > leaving aside the heuristics I came up with for a moment?
>
> The problem isn't that we might apply the heuristic once, that'd be fine. But
> that there's nothing preventing it from applying until there basically are no
> tuples left, as long as the vacuum is frequent enough.
>
> As a demo: The attached sql script ends up with a table containing 10k rows,
> but relpages being set 1 million.
I saw that too. But then I checked again a few seconds later, and
autoanalyze had run, so reltuples was 10k. Just like it would have if
there was no VACUUM statements in your script.
--
Peter Geoghegan