Re: Planning counters in pg_stat_statements (using pgss_store)

On Thu, Mar 26, 2020 at 02:22:47PM +0100, Julien Rouhaud wrote:
> On Thu, Mar 26, 2020 at 08:08:35PM +0900, Fujii Masao wrote:
> > 
> > Here are other comments.
> > 
> > -        if (jstate)
> > +        if (kind == PGSS_JUMBLE)
> > 
> > Why is PGSS_JUMBLE necessary? ISTM that we can still use jstate here, instead.
> > 
> > If it's ok to remove PGSS_JUMBLE, we can define PGSS_NUM_KIND(=2) instead
> > and replace 2 in, e.g., total_time[2] with PGSS_NUM_KIND. Thought?
> 
> Yes, we could be using jstate here.  I originally used that to avoid passing
> PGSS_EXEC (or the other one) as a way to say "ignore this information as
> there's the jstate which says it's yet another meaning".  If that's not an
> issue, I can change that as PGSS_NUM_KIND will clearly improve the explicit "2"
> all over the place.

Done, passing PGSS_PLAN when jumble is intended, with a comment saying that the
pgss_kind is ignored in that case.

> > +      <entry><structfield>total_time</structfield></entry>
> > +      <entry><type>double precision</type></entry>
> > +      <entry></entry>
> > +      <entry>
> > +        Total time spend planning and executing the statement, in milliseconds
> > +      </entry>
> > +     </row>
> > 
> > pg_stat_statements view has this column but the function not.
> > We should make both have the column or not at all, for consistency?
> > I'm not sure if it's good thing to expose the sum of total_plan_time
> > and total_exec_time as total_time. If some users want that, they can
> > easily calculate it from total_plan_time and total_exec_time by using
> > their own logic.
> 
> I think we originally added it as a way to avoid too much compatibility break,
> and also because it seems like a field most users will be interested in anyway.
> Now that I'm thinking about it again, I indeed think it was a mistake to have
> that in view part only.  Not mainly for consistency, but for users who would be
> interested in the total_time field while not wanting to pay the overhead of
> retrieving the query text if they don't need it.  So I'll change that!

Done

> > +        nested_level++;
> > +        PG_TRY();
> > 
> > In old thread [1], Tom Lane commented the usage of nested_level
> > in the planner hook. There seems no reply to that so far. What's
> > your opinion about that comment?
> > 
> > [1] https://www.postgresql.org/message-id/28980.1515803777@sss.pgh.pa.us
> 
> Oh thanks, I didn't noticed this part of the discussion.  I agree with Tom's
> concern, and I think that having a specific nesting level variable for the
> planner is the best workaround, so I'll implement that.

Done.

I also exported BufferUsageAccumDiff as mentioned previously, as it seems
clearner and will avoid future useless code churn, and run pgindent.

v10 attached.