Re: Showing primitive index scan count in EXPLAIN ANALYZE (for skip scan and SAOP scans)

On Tue, Aug 27, 2024 at 3:04 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Peter Geoghegan <pg(at)bowt(dot)ie> writes:
> > I see value in making it obvious to users when and how
> > pg_stat_all_indexes.idx_scan advances. Being able to easily relate it
> > to EXPLAIN ANALYZE output is useful, independent of whether or not
> > SAOPs happen to be used. That's probably the single best argument in
> > favor of showing "Index Searches: N" unconditionally. But I'm
> > certainly not going to refuse to budge over that.
>
> TBH, I'm afraid that this patch basically is exposing numbers that
> nobody but Peter Geoghegan and maybe two or three other hackers
> will understand, and even fewer people will find useful (since the
> how-many-primitive-scans behavior is not something users have any
> control over, IIUC). I doubt that "it lines up with
> pg_stat_all_indexes.idx_scan" is enough to justify the additional
> clutter in EXPLAIN. Maybe we should be going the other direction
> and trying to make pg_stat_all_indexes count in a less detailed but
> less surprising way, ie once per indexscan plan node invocation.

I kind of had that reaction too initially, but I think that was mostly
because "Primitive Index Scans" seemed extremely unclear. I think
"Index Searches" is pretty comprehensible, honestly. Why shouldn't
someone be able to figure out what that means?

Might make sense to restrict this to VERBOSE mode, too.

--
Robert Haas
EDB: http://www.enterprisedb.com