Thread

Re: Add a greedy join search algorithm to handle large join problems

Pavel Stehule <pavel.stehule@gmail.com> — 2025-12-11T06:12:29Z

čt 11. 12. 2025 v 3:53 odesílatel John Naylor <johncnaylorls@gmail.com>
napsal:

> On Wed, Dec 10, 2025 at 5:20 PM Tomas Vondra <tomas@vondra.me> wrote:
> > I did however notice an interesting thing - running EXPLAIN on the 99
> > queries (for 3 scales and 0/4 workers, so 6x 99) took this much time:
> >
> > master:       8s
> > master/geqo: 20s
> > master/goo:   5s
>
> > It's nice that "goo" seems to be faster than "geqo" - assuming the plans
> > are comparable or better. But it surprised me switching to geqo makes it
> > slower than master. That goes against my intuition that geqo is meant to
> > be cheaper/faster join order planning. But maybe I'm missing something.
>
> Yeah, that was surprising. It seems that geqo has a large overhead, so
> it takes a larger join problem for the asymptotic behavior to win over
> exhaustive search.
>

If I understand correctly to design - geqo should be slower for any queries
with smaller complexity. The question is how many queries in the tested
model are really complex.



>
> --
> John Naylor
> Amazon Web Services
>
>
>