Problems with sudden high load

Wednesday 10 January 2007 3:07:04 am

We have for the past weeks experienced extremely hight peaks in our CPU usage which we cannot explain. From a normal 2-8 % CPU usage on the database the CPU usage suddenly increases to 50-90% - without more users than ordinarily.
e.g.

Date                  user          idle         hits (otoba)

09:00:01 AM       2.04            96.99	         2685
09:10:01 AM       3.68            95.45	         2981
09:20:01 AM       6.23            92.51	         3771
09:30:01 AM       30.75          65.51	        4518
09:40:01 AM       82.15          10.57	        4573
09:50:01 AM       3.71            94.12	         4696
10:00:01 AM       4.70            94.08	          5801
10:10:01 AM       5.41            93.43	          3992

Restarting MySQL (and sometimes also clearing the entire cache) usually solves the problem.
We run a cluster solution with a powerfull database, 4 front end webservers and two load balancers.
As far as we can se the this CPU usage is not caused by more user traffic, but we cannot see what causes this extremely high load. Anyone else experience similar problems or any ideas ?
Whether or not this is related to another problem we have I do not know: see http://ez.no/community/forum/developer/database_inconsistency_replacement_of_attributes
Helle Andersen