What you are seeing is definitely neither normal nor right.
I am guessing that this is some Oracle-specific bug. We need to know what exactly those DB queries are. Actually, I wonder if you are hitting the issue Martín Langhoff identified a long time ago:
- https://moodle.org/mod/forum/discuss.php?d=120650#p530502
- https://moodle.org/mod/forum/discuss.php?d=143376#p653822
Really, if you can run Moodle on anything other than Oracle, you should. I would always opt for Postgres.
Note that there were some performance issues with 2.4.0, so if you can upgrade to 2.4.5, you should. However, those issues were nothing to do with the quiz module. (See https://moodle.org/mod/forum/discuss.php?d=227745 for details.)