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

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, vignesh21(at)gmail(dot)com, pryzby(at)telsasoft(dot)com, lukas(at)fittl(dot)com, alvherre(at)alvh(dot)no-ip(dot)org, magnus(at)hagander(dot)net, pgsql-hackers(at)postgresql(dot)org, thomas(dot)munro(at)gmail(dot)com, m(dot)sakrejda(at)gmail(dot)com
Subject: Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)
Date: 2023-02-27 19:58:30
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Melanie Plageman <melanieplageman(at)gmail(dot)com> writes:
> On Mon, Feb 27, 2023 at 10:30 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> The risk of needing to cast when using the "int" loop variable
>> as an enum is obviously the downside of that approach, but we have
>> not seen any indication that any compilers actually do warn.
>> It's interesting that you did see such a warning ... I wonder which
>> compiler you were using at the time?

> so, pretty much any version of clang I tried with
> -Wsign-conversion produces a warning.

> <source>:35:32: warning: implicit conversion changes signedness: 'int'
> to 'IOOp' (aka 'enum IOOp') [-Wsign-conversion]

Oh, interesting --- so it's not about the implicit conversion to enum
but just about signedness. I bet we could silence that by making the
loop variables be "unsigned int". I doubt it's worth any extra keystrokes
though, because we are not at all clean about sign-conversion warnings.
I tried enabling -Wsign-conversion on Apple's clang 14.0.0 just now,
and counted 13462 such warnings just in the core build :-(. I don't
foresee anybody trying to clean that up.

> I didn't do the casts in the attached patch since they aren't done elsewhere.

Agreed. I'll push this along with the earlier patch if there are
not objections.

regards, tom lane

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