cpu spike

Hi, Gurus,
I have oracle 9i R2 on Sun box with 4 cpus, my cron jobs usually run between 1:00am to 5:00am. Nobody is using databse during the night hours. This morning, I found that at 6:00am, the cpu number 4 spiked from 0% to 90% utilization for a few minutes and then down again. Could anybody tell me why and how can I find out why it happended? Thanks for help.

D.F.

Its possible that user Root was running some type of NICE process that was assigned to Cpu4. I would definately talk to the Unix admin. We had experienced database corruption once because one of the CPU was dying and loosing power.