MySQL over-loading, what could be causing this?

[James T Brock]

On my forum every couple of hours MySQL over-loads on my server and the load goes through the roof. My forum has a couple million posts and several thousand visitors a day.

Here is an example of the queries (hundreds of these per second)...

Query SELECT * FROM session WHERE sessionhash = 'dfd9268b20ae92b017c267ba18970a4b' AND lastactivity > 129440744
Query SELECT * FROM session WHERE sessionhash = 'bd05b6ddfc180f2012a7c741e0122488' AND lastactivity > 129440744
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query SELECT user.username, (user.options & 512) AS invisible, user.usergroupid, session.userid, session.inforu
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query UPDATE session SET lastactivity = 1294421744, location = '/forums/showthread.php?t=220501&page=2', in
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query SELECT COUNT(userID) AS c FROM session WHERE lastactivity > 1294421812 AND location LIKE '%gameroom%'
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query SELECT user.username, (user.options & 512) AS invisible, user.usergroupid, session.userid, session.inforu
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query UPDATE session SET lastactivity = 1294421802, location = '/forums/showthread.php?t=277163&page=3', in
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query SELECT COUNT(userID) AS c FROM session WHERE lastactivity > 1294421812 AND location LIKE '%gameroom%'
Query SELECT post.*, IF(post.visible = 2, 1, 0) AS isdeleted, editlog.userid AS edit_userid, editlog.dateline A
Query SELECT user.username, (user.options & 512) AS invisible, user.usergroupid, session.userid, session.inforu
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query SELECT * FROM session WHERE sessionhash = 'daddef1968276899ff4486a1c0b45fcf' AND lastactivity > 129440744
Query SELECT * FROM session WHERE sessionhash = '3599a066f604de7e17648eb96f68b3ba' AND lastactivity > 129440744
Query SELECT COUNT(userID) AS c FROM session WHERE lastactivity > 1294421812 AND location LIKE '%gameroom%'
Query UPDATE session SET lastactivity = 1294421729, location = '/forums/showthread.php?t=887806', inforum = 53,
Query UPDATE user SET lastactivity = 1294421729 WHERE userid = 9665
Query UPDATE user SET lastactivity = 1294421734 WHERE userid = 301320
Query UPDATE user SET lastactivity = 1294421734 WHERE userid = 301320
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei
Query INSERT INTO post (showsignature, allowsmilie, username, userid, title, pagetext, iconid, visible, parenti
Query INSERT IGNORE INTO session (sessionhash, userid, host, idhash, lastactivity, location, styleid, languagei

That's just a snapshot of what was just there. There are other queries as well that start showing up. Anyone familiar with vBulletin programming that has an idea of what could be happening when those queries are run? What exactly is happening when you see "user SET lastactivity" or "INSERT IGNORE INTO" Is that just a bunch of hits at one time, a DOS attack?