Re: Removing unneeded self joins

On Thu, Oct 19, 2023 at 6:16 AM Andrei Lepikhov
<a(dot)lepikhov(at)postgrespro(dot)ru> wrote:
> On 19/10/2023 01:50, Alexander Korotkov wrote:
> > This query took 3778.432 ms with self-join removal disabled, and
> > 3756.009 ms with self-join removal enabled. So, no measurable
> > overhead. Similar to the higher number of joins. Can you imagine
> > some extreme case when self-join removal could introduce significant
> > overhead in comparison with other optimizer parts? If not, should we
> > remove self_join_search_limit GUC?
> Thanks,
> It was Zhihong Yu who worried about that case [1]. And my purpose was to
> show a method to avoid such a problem if it would be needed.
> I guess the main idea here is that we have a lot of self-joins, but only
> few of them (or no one) can be removed.
> I can't imagine a practical situation when we can be stuck in the
> problems here. So, I vote to remove this GUC.

I've removed the self_join_search_limit. Anyway there is
enable_self_join_removal if the self join removal algorithm causes any
problems. I also did some grammar corrections for the comments. I
think the patch is getting to the committable shape. I noticed some
failures on commitfest.cputube.org. I'd like to check how this
version will pass it.

------
Regards,
Alexander Korotkov