[CentOS] Web server becoming unresponsive : high load

Hi,

I have a web server which is randomly becoming unresponsive.   I've checked
for hardware problems with no luck :
- no ethernet errors
- no disk errors
- no memory errors

So far I've managed to point the trouble at the web server since if I
restart httpd (apache) it comes back to normal.

This is not a shared server so I control (or at least like to think of) what
is hosted so I have two suspects:
a) my own code is behaving strangely.   For example, a php script that in a
given situation/parameters increases the usage.
b) some sort of attack.  Either in conjunction to a or other vulnerability.

I am looking for advices in how can I pin point since looking at every line
of code would be infeasible.

Centos 5.5 / apache / php 5.2.10
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.centos.org/pipermail/centos/attachments/20110311/7217d6d8/attachment.html>