Re: New statistics for tuning WAL buffer size

On 2020/10/01 12:56, Masahiro Ikeda wrote:
> 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

Understood. +1 to expose it as one function.


>> 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.

Thanks for updating the patch! LGTM.
Barring any other objection, I will commit it.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION