By default, when EP is installed using the autoinstaller, it enables SQL session state management.
When SQL Server support for session gets installed a job to delete the expired session is also installed, this job runs every minute and is called ASPState_Job_DeleteExpiredSessions;
It requires SQL Server Agent service to be running in order to work. Without this script running, you "ASPState" database could become huge and greatly affect the performance of EP.
By opening SQL Server Management Studio, and looking on the left panel where the server's objects are located you should see an item called SQL Server Agent, and below that an item called Jobs. You should see a job called ASPState_Job_DeleteExpiredSessions, and that the job is set to run.
SQL temp session database
FollowIf you are running EP on SQL Server Express, you should either switch to "InProc" session storage mode (in order to switch to that mode just comment out the "sqlConnectionString" parameter in EP Web.Config file) or email us with a workaround, since SQL Server Express edition does not include SQL Server Agent for running jobs.