Re: New statistics for tuning WAL buffer size

On Thu, Oct 1, 2020 at 6:53 AM Kyotaro Horiguchi
<horikyota(dot)ntt(at)gmail(dot)com> wrote:
>
> At Thu, 1 Oct 2020 09:05:19 +0900, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote in
> >
> >
> > On 2020/09/30 20:21, Amit Kapila wrote:
> > > 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:
> > >>> 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?
> >
> > We can adopt either of those approaches for pg_stat_wal. I think that
> > the former is a bit more flexible because we can collect only one of
> > WAL information even when pg_stat_wal will contain many information
> > in the future, by using the function. But you thought there are some
> > reasons that the latter is better for pg_stat_wal?
>
> FWIW I prefer to expose it by one SRF function rather than by
> subdivided functions. One of the reasons is the less oid consumption
> and/or reduction of definitions for intrinsic functions.
>
> Another reason is at least for me subdivided functions are not useful
> so much for on-the-fly examination on psql console. I'm often annoyed
> by realizing I can't recall the exact name of a function, say,
> pg_last_wal_receive_lsn or such but function names cannot be
> auto-completed on psql console. "select proname from pg_proc where
> proname like.. " is one of my friends:p On the other hand "select *
> from pg_stat_wal" requires no detailed memory.
>
> However subdivided functions might be useful if I wanted use just one
> number of wal-stats in a function, I think it is not a major usage and
> we can use a SQL query on the view instead.
>
> Another reason that I mildly want to object to subdivided functions is
> I was annoyed that a stats view makes many individual calls to
> functions that internally share the same statistics entry. That
> behavior required me to provide an entry-caching feature to my
> shared-memory statistics patch.
>

All these are good reasons to expose it via one function and I think
that is why most of our existing views also use one function approach.

--
With Regards,
Amit Kapila.