On Sun, 13 Jun 2021 at 21:28, Tomas Vondra <tomas.von...@enterprisedb.com> wrote: > > Here is a slightly updated version of the patch > > The main issue I ran into > is the special case clauselist_selectivity, which does > > if (list_length(clauses) == 1) > return clause_selectivity_ext(...); > > which applies to cases like "WHERE a < b" which can now be handled by > extended statistics, thanks to this patch. But clause_selectivity_ext > only used to call restriction_selectivity for these clauses, which does > not use extended statistics, of course. > > I considered either getting rid of the special case, passing everything > through extended stats, including cases with a single clause. But that > ends up affecting e.g. OR clauses, so I tweaked clause_selectivity_ext a > bit, which seems like a better approach.
Yeah, I looked at this a few months ago, while looking at the other extended stats stuff, and I came to the same conclusion that solving this issue by tweaking clause_selectivity_ext() is the best approach. I haven't looked at the patch in much detail yet, but I think the basic approach looks OK. There are a few comments that need updating, e.g.: - In statext_is_compatible_clause_internal(), before the "if (is_opclause(clause))" test. - The description of the arguments for examine_opclause_args(). I wonder if "expronleftp" for examine_opclause_args() should be "constonrightp", or some such -- as it stands it's being set to false for an Expr Op Expr clause, which doesn't seem right because there *is* an expression on the left. Regards, Dean
