Date: Tue, 21 Feb 2023 19:50:35 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Andres Freund <andres@anarazel.de>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, melanieplageman@gmail.com,
	vignesh21@gmail.com, lukas@fittl.com, alvherre@alvh.no-ip.org,
	magnus@hagander.net, pgsql-hackers@postgresql.org,
	thomas.munro@gmail.com, m.sakrejda@gmail.com
Subject: Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and
 more?)
Message-ID: <20230222015035.GQ1653@telsasoft.com>
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 <20230124223512.xqp7tjgqvzqokaxq@awork3.anarazel.de>
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On Sat, Feb 11, 2023 at 10:24:37AM -0800, Andres Freund wrote:
> On 2023-02-08 21:03:19 -0800, Andres Freund wrote:
> > Pushed the first (and biggest) commit. More tomorrow.
> 
> Just pushed the actual pg_stat_io view, the splitting of the tablespace test,
> and the pg_stat_io tests.

pg_stat_io says:

         * Some BackendTypes do not currently perform any IO in certain
         * IOContexts, and, while it may not be inherently incorrect for them to
         * do so, excluding those rows from the view makes the view easier to use.

        if (bktype == B_AUTOVAC_LAUNCHER && io_context == IOCONTEXT_VACUUM)
                return false;

        if ((bktype == B_AUTOVAC_WORKER || bktype == B_AUTOVAC_LAUNCHER) &&
                io_context == IOCONTEXT_BULKWRITE)
                return false;

What about these combinations?  Aren't these also "can't happen" ?

 relation      | bulkread   | autovacuum worker
 relation      | bulkread   | autovacuum launcher
 relation      | vacuum     | startup

-- 
Justin