On 20/5/2024 15:52, Andy Fan wrote:
Hi Andrei,
On 4/3/24 01:22, Tomas Vondra wrote:
Cool! There's obviously no chance to get this into v18, and I have stuff
to do in this CF. But I'll take a look after that.
I'm looking at your patch now - an excellent start to an eagerly awaited
feature!
A couple of questions:
1. I didn't find the implementation of strategy 'c' - estimation by the
number of distinct values. Do you forget it?
What do you mean the "strategy 'c'"?
As described in 0001-* patch:
* c) No extended stats with MCV. If there are multiple join clauses,
* we can try using ndistinct coefficients and do what eqjoinsel does.
2. Can we add a clauselist selectivity hook into the core (something
similar the code in attachment)? It can allow the development and
testing of multicolumn join estimations without patching the core.
The idea LGTM. But do you want
+ if (clauselist_selectivity_hook)
+ s1 = clauselist_selectivity_hook(root, clauses, varRelid,
jointype,
+
rather than
+ if (clauselist_selectivity_hook)
+ *return* clauselist_selectivity_hook(root, clauses, ..)
Of course - library may estimate not all the clauses - it is a reason,
why I added input/output parameter 'estimatedclauses' by analogy with
statext_clauselist_selectivity.
--
regards,
Andrei Lepikhov
Postgres Professional
