On 4/14/25 18:31, Robert Haas wrote:
On Tue, Apr 1, 2025 at 5:07 PM David Rowley <dgrowle...@gmail.com> wrote:
I tried to move things along to address Tom's concern about not
wanting to show this in EXPLAIN's standard output. I suggested in [1]
that we could use EXPLAIN ANALYZE, but nobody commented on that.
EXPLAIN ANALYZE is much more verbose than EXPLAIN already, and if we
put these in EXPLAIN ANALYZE then the viewer can more easily compare
planned vs actual. I had mentioned that Hash Join does something like
this for buckets.
Having looked at v6, I think it would help, at least if the reader is
sufficiently knowledgeable. From the values displayed, it looks like
someone could reconstruct the evict_ratio value in
cost_memoize_rescan(), and if they know the loop count, also the
hit_ratio. But that seems hard: if you weren't reading the code, how
would you know how to do it? Even if you are reading the code, are you
sure you'd reconstruct it correctly? I wonder why we think it's better
to display this than a more "cooked" number like the estimated hit
ratio that was proposed in v1?
+1.
My reasons: a) it more "physical"; b) We don't need to look for the
corresponding NestLoop JOIN node - my explans usually contain 150+ lines
and it is hard to get into the analysis something out of current screen.
--
regards, Andrei Lepikhov
