Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)

From: Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com>
To: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Lukas Fittl <lukas(at)fittl(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, pgsql-hackers(at)postgresql(dot)org, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, vignesh C <vignesh21(at)gmail(dot)com>
Subject: Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)
Date: 2023-01-18 06:10:38
Message-ID: CAOtHd0BYqEWWDrEPiEvZn9gELU1fSknFtAODcCVKFbtcxOMkbA@mail.gmail.com
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On Tue, Jan 17, 2023 at 9:22 AM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
> On Mon, Jan 16, 2023 at 4:42 PM Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com> wrote:
> > I missed a couple of versions, but I think the docs are clearer now.
> > I'm torn on losing some of the detail, but overall I do think it's a
> > good trade-off. Moving some details out to after the table does keep
> > the bulk of the view documentation more readable, and the "inform
> > database tuning" part is great. I really like the idea of a separate
> > Interpreting Statistics section, but for now this works.
> >
> > >+ <literal>vacuum</literal>: I/O operations performed outside of shared
> > >+ buffers while vacuuming and analyzing permanent relations.
> >
> > Why only permanent relations? Are temporary relations treated
> > differently? I imagine if someone has a temp-table-heavy workload that
> > requires regularly vacuuming and analyzing those relations, this point
> > may be confusing without some additional explanation.
>
> Ah, yes. This is a bit confusing. We don't use buffer access strategies
> when operating on temp relations, so vacuuming them is counted in IO
> Context normal. I've added this information to the docs but now that
> definition is a bit long. Perhaps it should be a note? That seems like
> it would draw too much attention to this detail, though...

Thanks for clarifying. I think the updated definition still works:
it's still shorter than the `normal` context definition.

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