Re: Trigger more frequent autovacuums of heavy insert tables

On Tue, Feb 25, 2025 at 11:03 AM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
> This does however leave me with the question of how to handle the
> original question of whether or not to cap the proposed relallfrozen
> to the value of relallvisible when updating stats at the end of
> vacuum. The current code in heap_vacuum_rel() caps relallvisible to
> relpages, so capping relallfrozen to relallvisible would follow that
> pattern. However, the other places relallvisible is updated do no such
> capping (do_analyze_rel(), index_update_stats()). It doesn't seem like
> there is a good reason to do it one place and not the others. So, I
> suggest either removing all the caps and adding a WARNING or capping
> the value in all places. Because users can now manually update these
> values in pg_class, there wouldn't be a way to detect the difference
> between a bogus relallfrozen value due to VM corruption or a bogus
> value due to manual statistics intervention. This led me to think that
> a WARNING and no cap would be more effective for heap_vacuum_rel().

I mean, does it really make any difference one way or the other?

Given that users could manually update the catalog, we have to be able
to tolerate bad data in the catalogs without the world ending. If that
code has to exist anyway, then it's not mandatory to cap. On the other
hand, there's no great virtue in refusing to correct data that we know
to be wrong. Unless there is some other consideration which makes one
way better than the other, this feels like author's choice.

--
Robert Haas
EDB: http://www.enterprisedb.com