What causes these queries and can they be optimized? session table
 

Code:
Query Copying to t SELECT ... FROM session AS session LEFT JOIN user AS user ON(user.userid = session.userid) WHERE session.lastactivity > 1282336220 ORDER BY username ASC, lastactivity DESC
Query Copying to t SELECT ... FROM session AS session LEFT JOIN user AS user ON(user.userid = session.userid) WHERE session.lastactivity > 1282336219 ORDER BY username ASC, lastactivity DESC
Query Copying to t SELECT ... FROM session AS session LEFT JOIN user AS user ON(user.userid = session.userid) WHERE session.lastactivity > 1282336219 ORDER BY username ASC, lastactivity DESC
I see these all the time using mtop and often the server will process 60 or so queries like this at the exact same time sending the load on the server very high.

Any ideas?