Re: WAL usage calculation patch

On Sat, Apr 4, 2020 at 11:33 AM Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
>
> On Sat, Apr 04, 2020 at 10:38:14AM +0530, Amit Kapila wrote:
>
> > > The patch-2 might need to be
> > > rebased if the other related patch [2] got committed first and we
> > > might need to tweak a bit based on the input from other thread [1]
> > > where we are discussing user interface for it.
> > >
> >
> > The primary question for patch-2 is whether we want to include WAL
> > usage information for the planning phase as we did for BUFFERS in
> > recent commit ce77abe63c (Include information on buffer usage during
> > planning phase, in EXPLAIN output, take two.). Initially, I thought
> > it might be a good idea to do the same for WAL but after reading the
> > thread that leads to commit, I am not sure if there is any pressing
> > need to include WAL information for the planning phase. Because
> > during planning we might not write much WAL (with the exception of WAL
> > due to setting of hint-bits) so users might not care much. What do
> > you think?
>
>
> I agree that WAL activity during planning shouldn't be very frequent, but it
> might still be worthwhile to add it.
>

We can add if we want but I am not able to convince myself for that.
Do you have any use case in mind? I think in most of the cases
(except for hint-bit WAL) it will be zero. If we are not sure of this
we can also discuss it separately in a new thread once this
patch-series is committed and see if anybody else sees the value of it
and if so adding the code should be easy.

> I'm wondering how stable the normalized
> WAL information would be in some regression tests, as the counters are only
> showed if non zero. Maybe it'd be better to remove them from the output, same
> as the buffers?
>

Which regression tests are you referring to? pg_stat_statements? If
so, why would it be unstable? It should always generate WAL although
the exact values may differ and we have already taken care of that in
the patch, no?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com