So my friend Paul shown me how to troubleshoot fastCGI on plesk boxes, very easy..
# pstree | grep cgi | `-httpd---20*[php-cgi]
We can see that 20 php-cgi processes run. If we check the maximum in the configuration file set for fastCGI of Apache2..
# cat /etc/httpd/conf.d/fcgid.conf | grep MaxProc FcgidMaxProcesses 20
We see 20 is the maximum, so it’s definitely hitting the FastCGI limit, we need to increase the limits, so we just edit the file and increase the limits for that variable;
vi /etc/httpd/conf.d/fcgid.conf echo "FcgidMaxProcesses 50" >> /etc/httpd/conf.d/fcgid.conf