Re: Custom pgstat support performance regression for simple queries

On Wed, Jul 23, 2025 at 05:09:54PM +0900, Michael Paquier wrote:
> On Jul 23, 2025, at 16:33, Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> > Maybe we could use a flag, say:
> >
> > #define PGSTAT_PENDING_IO (1 << 0)
> > #define PGSTAT_PENDING_WAL (1 << 1)
> > #define PGSTAT_PENDING_SLRU (1 << 2)
> >
> > and check for a pgstat_pending_mask in pgstat_report_stat() instead?
> >
> > They would need to set pgstat_pending_mask accordingly when they flush, have
> > pending stats though.
>
> The point is just to say to the report path to move further if at least one of
> the fixed stats kinds has something to flush, then let the loop do its work
> across all the stats kinds if they have a flush callback,

Right.

> so we don’t really need to mix multiple numbers; we could just have a single
> boolean flag that any fixed-sized stats kinds can set to let the reporting know
> that some activity has happened.

That works to say "there are pending stats" but not well to say "there are no
pending stats".

Indeed, with a single boolean flag, then how could a stat say that it has nothing
pending anymore (when flushing) without saying "all the stats have nothing
pending" (while some may still have pending stats)?

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
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