Re: Add callbacks for fixed-numbered stats flush in pgstats

Hi,

On Wed, Sep 04, 2024 at 03:12:37PM +0900, Michael Paquier wrote:
> On Wed, Sep 04, 2024 at 05:28:56AM +0000, Bertrand Drouvot wrote:
> > On Wed, Sep 04, 2024 at 02:05:46PM +0900, Kyotaro Horiguchi wrote:
> >> The generalization sounds good to me, and hiding the private flags in
> >> private places also seems good.
> >
> > +1 on the idea.
>
> Thanks for the feedback.
>
> >> Regarding pgstat_io_flush_cb, I think it no longer needs to check the
> >> have_iostats variable, and that check should be moved to the new
> >> pgstat_flush_io(). The same applies to pgstat_wal_flush_cb() (and
> >> pgstat_flush_wal()). As for pgstat_slru_flush_cb, it simply doesn't
> >> need the check anymore.
> >
> > Agree. Another option could be to add only one callback (the flush_fixed_cb one)
> > and get rid of the have_fixed_pending_cb one. Then add an extra parameter to the
> > flush_fixed_cb that would only check if there is pending stats (without
> > flushing them). I think those 2 callbacks are highly related that's why I
> > think we could "merge" them, thoughts?
>
> I would still value the shortcut that we can use if there is no
> activity to avoid the clock check with GetCurrentTimestamp(),

Agree. The idea was to add an additional parameter (say "check_only") to the
flush_fixed_cb. If this parameter is set to true then the flush_fixed_cb would
do nothing (no flush at all) but return a boolean that would indicate if there
is pending stats. In case it returns false, then we could avoid the clock check.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
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