Apache not using all available slots?

Question

Apache HTTP Server

Gentlemen, there is the following situation: Apache is configured to run a large number of processes, but in fact it launches only 4. As a result, 4 processes are closed and the site slows down. What could be the problem?
Everything works on VDS with CentOS + Nginx + Apache/2.2.3
Apache uses the prefork module, here is the configuration piece:
<IfModule prefork.c>
MaxKeepAliveRequests 100
KeepAliveTimeout 5
ServerLimit 50
StartServers 15
MinSpareServers 15
MaxSpareServers 20
MaxClients 50
MaxRequestsPerChild 500
server-status gives approximately following:
WW__.......................
Srv PID Acc M CPU SS Req Conn Child Slot
0-1 13520 0/87/90 W 19.02 0 0 0.0 0.15 0.15 1-1 22246
0/13/113 W 7.95 9 0 0.0 0.06 0.99
2-1 13522 0/96/107 _ 21.55 0 0 0.0 0.3
1 17913 0/51/151 _ 15.45 0 0 0.0 0.09 0.44
i.e. only the first four slots (WW__) always work, the rest are resting. Always.
No limits are set in /etc/security/limits.conf.
There are no errors in the Apache logs.
Any suggestions for where else to look?

Answer 1

As often happens, everything turned out to be much simpler)
I looked at the settings and changed them only in the /etc/httpd/conf/httpd.conf file (which is actually used).
But it turned out that everything related to the prefork, although it was indicated in the main file, was also duplicated in a separate file /etc/httpd/conf.d/prefork.conf - I didn’t notice it right away = \
Thank you all for your help, plus you karma! :)

Answer 2

1. KeepAlive off
2. Set ab on some simpler script (like <?phpinfo();?>) with 10 simultaneous connections - I'm sure there will be 10 connections.