Re: Removing unneeded self joins

On Thu, Oct 19, 2023 at 6:16 AM Andrei Lepikhov
<a.lepikhov@postgrespro.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.

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Regards,
Alexander Korotkov