samba - Oct 2014 - User deletion of Samba4 is slow?

Hi,

I noticed the mysterious phenomenon! It took tens minutes to delete
thousands of users.
The same result was obtained although I checked by ldbdel besides samba-tool.

If a lot of additions and deletion are repeated, the tendency for
deletion to become slow will be seen.
This tendency has not been improved although I also tried the reboot
of Samba or OS.

Please teach me how to improve.

Thanks,