Apache: The Definitive Guide, Second Edition

3.6. Controlling Virtual Hosts on Unix

When started without the - X flag, which is what you would do in real operation, Apache launches a number of child versions of itself so that any incoming request can be instantly dealt with. This is an excellent scheme, but we need some way of controlling this sprawl of software. The necessary directives are there to do it.

3.6.1. MaxClients

               
               
               
               MaxClients number
Default number: 150
Server config

This directive limits the number of requests that will be dealt with simultaneously. In the current version of Apache, this effectively limits the number of servers that can run at one time.

3.6.2. MaxRequestsPerChild

               
               
               
               MaxRequestsPerChild number
Default number: 30
Server config

Each child version of Apache handles this number of requests and dies (unless the value is 0, in which case it will last forever or until the machine is rebooted). It is a good idea to set a number here so that any accidental memory leaks in Apache are tidied up. Although there are no known leaks in Apache, it is not impossible for them to occur in the system libraries, so it is probably wise not to disable this unless you are absolutely sure the code is byte-tight.

3.6.3. MaxSpareServers

               MaxSpareServers number
Default number: 10
Server config

No more than this number of child servers will be left running and unused. Setting this to an unnecessarily large number is a bad idea, since it depletes resources needlessly. How many is too many depends on which modules ...