| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
| Cc: | Robert Treat <rob(at)xzilla(dot)net>, Michael Paquier <michael(at)paquier(dot)xyz>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Revive num_dead_tuples column of pg_stat_progress_vacuum |
| Date: | 2024-06-19 01:16:43 |
| Message-ID: | CAH2-WzmyzRggrr_+yo5FrZCorwRT=LpipRgraYb=EPWYRqCH5g@mail.gmail.com |
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On Tue, Jun 18, 2024 at 8:49 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > At least I couldn't find anywhere in the docs where we have
> > described the relationship between these columns before. Thoughts?
>
> It would be a good idea to improve the documentation, but I think that
> we cannot simply compare these two numbers since the numbers that
> these fields count are slightly different. For instance,
> pg_stat_all_tables.n_dead_tup includes the number of dead tuples that
> are going to be HOT-pruned.
This isn't a small difference. It's actually a huge one in many cases:
Practically speaking they're just two different things, with hardly
any fixed relationship.
--
Peter Geoghegan
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