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

On 2020/10/01 13:35, Fujii Masao wrote:
> 
> 
> 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.

I updated typedefs.list and pushed the patch. Thanks!

Regards,

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