by Ken Task.
When was the last time checked health of your DB?
Suggest you install MySQLTuner.pl - a perl script and run with superuser creds (root). That is not a Moodle tool/plugin ... it's outside of Moodle.
That will report from stats your DB server has been keeping all along. It also provides suggested recommendations on what config changes to make to improve DB health/performance.
'SoS', Ken