Re: Showing I/O timings spent reading/writing temp buffers in EXPLAIN

Hi,

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, August 24th, 2021 at 13:20, Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> wrote:

> Em ter., 24 de ago. de 2021 às 03:11, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> escreveu:
>
> > On Mon, Aug 23, 2021 at 10:46 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > >
> > > On Thu, Aug 19, 2021 at 10:52 PM Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> wrote:
> > > >
> > > > Em qui., 19 de ago. de 2021 às 09:21, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> escreveu:
> > > >>
> > > >> Hi all ,
> > > >>
> > > >> It's reported on pgsql-bugs[1] that I/O timings in EXPLAIN don't show

<snip>

> >
> > I've attached the updated patch that incorporates the above comment.
>
> The patch looks fine to me.
>

The patch looks good to me too. However I do wonder why the timing is added only on
the

if (es->format == EXPLAIN_FORMAT_TEXT)

block and is not added when, for example, the format is json. The instrumentation has
clearly recorded the timings regardless of the output format.

Also, it might be worth while to consider adding some regression tests. To my
understanding, explain.sql provides a function, explain_filter, which helps create
a stable result. For example, such a test case can be:

set track_io_timing = 'on';
select explain_filter('explain (analyze, buffers) select count(*) from generate_series(1,100000)');

then it would be enough to verify that the line:

I/O Timings: temp read=N.N write=N.N

is present. The above would apply on the json output via `explain_filter_to_json`
of course.

Thoughts?

Cheers,
//Georgios