On Sat, 29 Jun 2019 at 10:06, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> > On 2019-Apr-03, Tom Lane wrote:
> >> Ping? If nobody has any further ideas here, I'm going to clean up
> >> the regression test issue and push this.
>
> > Is this still live? If so, is it something for pg12?
>
> It's still live --- Rowley seemed not happy with my proposal so
> I didn't push it. I'm not sure that it's must-fix-for-v12;
> the problem is older than that.
One thing we could look at would be to charge an additional
cpu_tuple_cost per outer row for all joins except semi, anti and
unique joins. This would account for the additional lookup for
another matching row which won't be found and cause the planner to
slightly favour keeping the unique rel on the inner side of the join,
when everything else is equal.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services