Re: New statistics for tuning WAL buffer size

On Tue, Sep 29, 2020 at 9:23 PM Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
>
> On 2020/09/29 11:51, Masahiro Ikeda wrote:
> > On 2020-09-29 11:43, Amit Kapila wrote:
> >> On Tue, Sep 29, 2020 at 7:39 AM Masahiro Ikeda <ikedamsh(at)oss(dot)nttdata(dot)com> wrote:
> >>>
> >>> On 2020-09-28 12:43, Amit Kapila wrote:
> >>> > On Mon, Sep 28, 2020 at 8:24 AM Kyotaro Horiguchi
> >>> > <horikyota(dot)ntt(at)gmail(dot)com> wrote:
> >>> >>
> >>> >> At Mon, 28 Sep 2020 08:11:23 +0530, Amit Kapila
> >>> >> <amit(dot)kapila16(at)gmail(dot)com> wrote in
> >>> >> > One other thing that occurred to me today is can't we keep this as
> >>> >> > part of PgStat_GlobalStats? We can use pg_stat_reset_shared('wal'); to
> >>> >> > reset it. It seems to me this is a cluster-wide stats and somewhat
> >>> >> > similar to some of the other stats we maintain there.
> >>> >>
> >>> >> I like that direction, but PgStat_GlobalStats is actually
> >>> >> PgStat_BgWriterStats and cleard by a RESET_BGWRITER message.
> >>> >>
> >>> >
> >>> > Yeah, I think if we want to pursue this direction then we probably
> >>> > need to have a separate message to set/reset WAL-related stuff. I
> >>> > guess we probably need to have a separate reset timestamp for WAL. I
> >>> > think the difference would be that we can have one structure to refer
> >>> > to global_stats instead of referring to multiple structures and we
> >>> > don't need to issue separate read/write calls but OTOH I don't see
> >>> > many disadvantages of the current approach as well.
> >>>
> >>> IIUC, if we keep wal stats as part of PgStat_GlobalStats,
> >>> don't we need to add PgStat_ArchiverStats and PgStat_SLRUStats
> >>> to PgStat_GlobalStats too?
> >>>
> >>
> >> I have given the idea for wal_stats because there is just one counter
> >> in that. I think you can just try to evaluate the merits of each
> >> approach and choose whichever you feel is good. This is just a
> >> suggestion, if you don't like it feel free to proceed with the current
> >> approach.
> >
> > Thanks for your suggestion.
> > I understood that the point is that WAL-related stats have just one counter now.
> >
> > Since we may add some WAL-related stats like pgWalUsage.(bytes, records, fpi),
> > I think that the current approach is good.
>
> +1
>

Okay, it makes sense to keep it in the current form if we have a plan
to extend this view with additional stats. However, why don't we
expose it with a function similar to pg_stat_get_archiver() instead of
providing individual functions like pg_stat_get_wal_buffers_full() and
pg_stat_get_wal_stat_reset_time?

--
With Regards,
Amit Kapila.