By default in apache has set the Max_Connection =256, also if you want to raise your client limit like 512. Open the httpd.conf file and add the below lines,

# vim /etc/httpd/conf/httpd.conf



MaxClients 512

ServerLimit 512

Finally restart your httpd service.

If need to calculate the total active http connections, use this command,
 
# netstat -nap | grep :80 


tcp        0      0 0.0.0.0:80                  0.0.0.0:*            LISTEN      2663/httpd          

tcp        0      0 192.168.1.50:80           192.168.1.5:28225      SYN_RECV    -                   

tcp        0      0 192.168.1.50:80           192.168.1.90:1916      SYN_RECV    -                   

tcp        0      0 192.168.1.50:80           192.168.1.8:64631      SYN_RECV    -                   

tcp        0      0 192.168.1.50:80           192.168.1.48:36603     SYN_RECV    -  
                 
If you need to watch current running process every 2 seconds,
 
# watch "pgrep httpd"


Every 2.0s: pgrep httpd                              Thu Jul 30 12:31:11 2015



2656

2663

8096

8845

14616

16565

If you want to count the number of connection's
 
# pgrep httpd | wc -l
20


Number of request to your server,
 
# netstat -anp | grep 80| awk {'print $5'} | cut -d":" -f1 | sort | uniq -c | wc -l

Also get current connection with logs,
 
# tail -f /var/log/apache2/access.log

MySQL:

Also to know the MySQL database maximum connections in your system,
 
# mysqladmin -u root variables | grep max_connections

or
# mysqladmin -u root variables | grep max_connections | awk '{print $4}'