On 12/9/2024 16:57, Tomas Vondra wrote:
On 9/12/24 12:12, David Rowley wrote:
On Thu, 12 Sept 2024 at 21:51, Andrei Lepikhov <lepi...@gmail.com> wrote:
but doesn't estimate_num_groups()
supposed to already do that? The comment says:
* 3. If the list contains Vars of different relations that are known equal
* due to equivalence classes, then drop all but one of the Vars from each
* known-equal set, keeping the one with smallest estimated # of values
* (since the extra values of the others can't appear in joined rows).
* Note the reason we only consider Vars of different relations is that
* if we considered ones of the same rel, we'd be double-counting the
* restriction selectivity of the equality in the next step.
I haven't debugged this, but how come this doesn't do the trick?
I've got your point now.
Unfortunately, this comment says that estimate_num_groups removes
duplicates from the list of grouping expressions (see
exprs_known_equal). But it doesn't discover em_members to find the
most-fitted clause for each grouping position.
--
regards, Andrei Lepikhov
