Re: BUG #16109: Postgres planning time is high across version (Exposebuffer usage during planning in EXPLAIN)

On Fri, Jan 24, 2020 at 6:55 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
>
> On Wed, Nov 13, 2019 at 11:39:04AM +0100, Julien Rouhaud wrote:
> > (moved to -hackers)
> >
> > On Tue, Nov 12, 2019 at 9:55 PM Andres Freund <andres@anarazel.de> wrote:
> > >
> > > This last point is more oriented towards other PG developers: I wonder
> > > if we ought to display buffer statistics for plan time, for EXPLAIN
> > > (BUFFERS). That'd surely make it easier to discern cases where we
> > > e.g. access the index and scan a lot of the index from cases where we
> > > hit some CPU time issue. We should easily be able to get that data, I
> > > think, we already maintain it, we'd just need to compute the diff
> > > between pgBufferUsage before / after planning.
> >
> > That would be quite interesting to have.  I attach as a reference a
> > quick POC patch to implement it:
>
> +1
>
> +       result.shared_blks_hit = stop->shared_blks_hit - start->shared_blks_hit;
> +       result.shared_blks_read = stop->shared_blks_read - start->shared_blks_read;
> +       result.shared_blks_dirtied = stop->shared_blks_dirtied -
> +               start->shared_blks_dirtied;
> [...]
>
> I think it would be more readable and maintainable using a macro:
>
> #define CALC_BUFF_DIFF(x) result.##x = stop->##x - start->##x
> CALC_BUFF_DIFF(shared_blks_hit);
> CALC_BUFF_DIFF(shared_blks_read);
> CALC_BUFF_DIFF(shared_blks_dirtied);
> ...
> #undefine CALC_BUFF_DIFF

Good idea.  Note that you can't use preprocessor concatenation to
generate something else than a token or a number, so the ## can just
be removed here.