High server load

[hlds]

Sometimes my website is down due to high server load.
htop screenshot:
http://img703.imageshack.us/img703/4042/highcpupad.png

Sometimes there are php5-fpm processes that take 100% CPU. Why? It
slowes down everything. I also get mysql database errors (too many
connections).

How can I determine what causes this?
thanks

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,206471,206471#msg-206471