Hi Sergei, that would be great as well and i was actually looking to emulate off switch using threshold so sure, optimizer switch seems to make more sense. I'm just looking for any way of disabling this optimization without recompiling the server if possible. 

Thanks, 
Slawomir

Dnia 16 sierpnia 2019 17:14 Sergei Golubchik <serg@mariadb.org> napisał(a):

Hi, Slawomir!

On Aug 13, pslawek83 wrote:
Hi Guys, is in_predicate_conversion_th going to be re-enabled for
release builds in some next mariadb release? If I make pull request,
will you take it?     Basically for everyone not aware about the
issue, this forced IN-predicate to subquery conversion is
de-generating some simple queries so badly that they start to take
couple of hours instead of seconds, and there is currently no way of
fixing these queries nor to turn this conversion off.
Thanks,
Slawomir.

Perhaps instead of in_predicate_conversion_threshold, we'd better add
an optimizer switch to disable this optimization?

I've commented in https://jira.mariadb.org/browse/MDEV-16871

Regards,
Sergei
VP of MariaDB Server Engineering
and security@mariadb.org