Heavy CPU loads with numerous apache tasks

[etrader]

My server usually works well with 1-5% of CPU usage, and in this condition top command shows few apache tasks (e.g. 5, comparable to the number of visitors), and several root tasks.

 

But sometimes (with a higher traffic, but not too much, e.g. double), the CPU usage goes to 70% and top commands shows numerous apache tasks, each using 1-3% CPU and 30-40% for mysql.

 

In this condition, the server is almost dead as it is hard to connect to the mysql database.

 

I believe this problem is not due to higher usage of the server by higher traffic, but suddenly increased traffic force apache to do other tasks. When the CPU usage increases, even by making the website offline (0 traffic), the CPU usage hardly goes down. In addition, re-boot does not resolve this heavy load.

 

Do you have any idea ?