A Flooded Session Table Can Dramatically Slow Down Your Joomla Site

The short term solution was simple, we only needed to truncate the table (e.g. delete the all the rows in that table and completely reset its indexes), we did this by issuing the following command in phpMyAdmin:

TRUNCATE TABLE #__session

(Note: If you want to use the above command, then you will need to replace #__ with your table prefix.)