If you did TOP in ssh, and noticed httpd process has a high cpu load, and has been running for a long time (e.g. over 5 minutes) then you might try lowering your MaxRequestsPerChild.
vi /etc/httpd/conf/extra/httpd-mpm.conf
Now change your MaxRequestsPerChild from 1000 to 20...
<IfModule mpm_prefork_module>
StartServers 5
MinSpareServers 10
MaxSpareServers 20
ServerLimit 812
MaxClients 812
MaxRequestsPerChild 20
</IfModule>
service httpd restart
Apache.conf
To start, open the Apache configuration file and locate the directives section:
On a DirectAdmin based server it will be located in: /etc/httpd/conf/extra/httpd-mpm.conf
On a cPanel server, it will be located in /usr/local/apache/conf/
On a Plesk server, it will be in /etc/httpd/conf/
