Improving mod_perl Driven Site's Performance -- Part VII: Performance Tuning by Tweaking Apache Configuration
Correct configuration of the MinSpareServers, MaxSpareServers, StartServers, MaxClients, and MaxRequestsPerChild parameters is very important. There are no defaults. If they are too low, you will under-use the system's capabilities. If they are too high, the chances are that the server will bring the machine to its knees.