Re: New statistics for tuning WAL buffer size

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:
>> 
>> On 2020-09-28 12:43, Amit Kapila wrote:
>> > On Mon, Sep 28, 2020 at 8:24 AM Kyotaro Horiguchi
>> > <horikyota.ntt@gmail.com> wrote:
>> >>
>> >> At Mon, 28 Sep 2020 08:11:23 +0530, Amit Kapila
>> >> <amit.kapila16@gmail.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.

-- 
Masahiro Ikeda
NTT DATA CORPORATION