Error: "mod_fcgid: can't apply process slot for" makes my server unresponsive for a period of time Following error keeps appearing in my PHP error_log

mod_fcgid: can't apply process slot for


So far I pinpointed this issue to following settings in httpd.conf

FcgidMaxProcessesPerClass 8
FcgidMaxProcesses 20


By default these settings were set to 8 and 20, this would result in periodical freezes of my server (2 times per hour for 1 - 2 minutes).

I modified these settings to the following

FcgidMaxProcessesPerClass 1000
FcgidMaxProcesses 1000


With these new settings of 1000 each, server freezes occur only once per day but for as long as 10 - 30 minutes. 

--What I mean by server freezes--

Both PHP and MySQL server is unresponsive. 500 error is returned to the client after a minute or longer.

This freezing behavior stop completely on its own, everything goes back to normal after stated time above.

High server load is not likely to be the issue, since these freezes occur randomly each day. Both CPU and RAM is at 3% - 6% when freezes occur.
There is surprisingly little information about this error out there.

My server provider suggested that FastCGI might be a poor PHP interpreter for potentially high traffic websites. I switched my interpreter to NGINX with support of PHP-FPM. 

I dont have enough data yet to confirm that freezing was solved completely (but now it wont be related to FastCGI), NGINX is the preferred option for maintaining high performance server as suggested by various sources.