Re: New statistics for tuning WAL buffer size - Mailing list pgsql-hackers

On 2020-10-01 11:33, Amit Kapila wrote:
> On Thu, Oct 1, 2020 at 6:53 AM Kyotaro Horiguchi
> <horikyota.ntt@gmail.com> wrote:
>> 
>> At Thu, 1 Oct 2020 09:05:19 +0900, Fujii Masao 
>> <masao.fujii@oss.nttdata.com> wrote in
>> >
>> >
>> > On 2020/09/30 20:21, Amit Kapila wrote:
>> > > On Tue, Sep 29, 2020 at 9:23 PM Fujii Masao
>> > > <masao.fujii@oss.nttdata.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@oss.nttdata.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.

Thanks for your comments.
I didn't notice there are the above disadvantages to provide individual 
functions.

I changed the latest patch to expose it via one function.

Regards,
-- 
Masahiro Ikeda
NTT DATA CORPORATION