Re: SLRU statistics

On Tue, 21 Jan 2020 at 01:38, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>
> On Mon, Jan 20, 2020 at 01:04:33AM +0000, tsunakawa(dot)takay(at)fujitsu(dot)com wrote:
> >From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
> >> One of the stats I occasionally wanted to know are stats for the SLRU
> >> stats (we have couple of those - clog, subtrans, ...). So here is a WIP
> >> version of a patch adding that.

+1

> >
> >How can users take advantage of this information? I think we also need
> >the ability to set the size of SLRU buffers. (I want to be freed from
> >the concern about the buffer shortage by setting the buffer size to its
> >maximum. For example, CLOG would be only 1 GB.)
> >
>
> You're right the users can't really take advantage of this - my primary
> motivation was providing a feedback for devs, benchmarking etc. That
> might have been done with DEBUG messages or something, but this seems
> more convenient.

I've not tested the performance impact but perhaps we might want to
disable these counter by default and controlled by a GUC. And similar
to buffer statistics it might be better to inline
pgstat_count_slru_page_xxx function for better performance.

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
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