Re: Fix CPU cost of right-semi and right-anti hash joins

Hi Richard

>
> > hashjointuples is the third count for all of the semi/anti join types.
> > That's exactly right for otherquals and cpu_tuple_cost, but wrong for
> > joinquals. For plain joins it is the second count, so there the
> > charge is right for joinquals and pessimistic for otherquals. That is
> > also what the comment below means:
> I found an older explanation from Tom Lane that seems relevant here:
> https://postgr.es/m/21225.1371131974@sss.pgh.pa.us
>
> He points out that costing joinrestrictinfo “returns the costs for ALL
> the quals”, and that after subtracting hash_qual_cost, qp_qual_cost represents
> all additional clauses beside the hash clauses.
>
> So in this case qp_qual_cost combines two executor qual classes with
> different evaluation populations: non-hash joinquals and pushed-down
> otherquals. It therefore seems that changing the multiplier for the combined
> qp_qual_cost cannot in general make both parts correct.
>
> Would it make sense to split those two costs before applying the
> right-anti candidate-pair multiplier?
>
>
>
Thanks