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

Hi,

On 2023-03-06 14:24:09 -0500, Melanie Plageman wrote:
> On Mon, Mar 06, 2023 at 11:09:19AM -0800, Andres Freund wrote:
> > On 2023-03-06 10:09:24 -0500, Melanie Plageman wrote:
> > > On Mon, Mar 6, 2023 at 1:48 AM Kyotaro Horiguchi
> > > <horikyota(dot)ntt(at)gmail(dot)com> wrote:
> > > >
> > > > At Mon, 06 Mar 2023 15:24:25 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
> > > > > In any case, I think we need to avoid such concurrent autovacuum/analyze.
> > > >
> > > > If it is correct, I believe the attached fix works.
> > >
> > > Thanks for investigating this!
> > >
> > > Yes, this fix looks correct and makes sense to me.
> >
> > Wouldn't it be better to just perform the section from the ALTER TABLE till
> > the DROP TABLE in a transaction? Then there couldn't be any other accesses in
> > just that section. I'm not convinced it's good to disallow all concurrent
> > activity in other parts of the test.
>
> You mean for test coverage reasons? Because the table in question only
> exists for a few operations in this test file.

That, but also because it's simply more reliable. autovacuum=off doesn't
protect against a anti-wraparound vacuum or such. Or a concurrent test somehow
triggering a read. Or ...

Greetings,

Andres Freund