| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tomas Vondra <tv(at)fuzzy(dot)cz>, Robert Haas <robertmhaas(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Decoupling antiwraparound autovacuum from special rules around auto cancellation |
| Date: | 2023-01-19 03:26:22 |
| Message-ID: | CAH2-Wzka6vefY1ymzyjRw3BU7tkMknYkn2oz_5M-ovX=av2f=w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Jan 18, 2023 at 7:04 PM Andres Freund <andres(at)anarazel(dot)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
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