On 5/23/24 09:04, Andy Fan wrote:
Andrei Lepikhov <a.lepik...@postgrespro.ru> writes:
* c) No extended stats with MCV. If there are multiple join clauses,
* we can try using ndistinct coefficients and do what eqjoinsel does.
OK, I didn't pay enough attention to this comment before. and yes, I get
the same conclusion as you - there is no implementation of this.
and if so, I think we should remove the comments and do the
implementation in the next patch.
I have an opposite opinion about it:
1. distinct estimation is more universal thing - you can use it
precisely on any subset of columns.
2. distinct estimation is faster - it just a number, you don't need to
detoast huge array of values and compare them one-by-one.
So, IMO, it is essential part of join estimation and it should be
implemented like in eqjoinsel.
Do you think the hook proposal is closely connected with the current
topic? IIUC it's seems not. So a dedicated thread to explain the problem
to slove and the proposal and the follwing discussion should be helpful
for both topics. I'm just worried about mixing the two in one thread
would make things complexer unnecessarily.
Sure.
--
regards,
Andrei Lepikhov
Postgres Professional
