KeepAlives and MaxClients

It is worth turning off KeepAlive (see Chapter 3) on busy sites because it keeps the server connected to each client for a minimum time even if they are doing nothing. This consumes processes, which consumes memory. Because each connection corresponds to a process, and each process has a whole instance of Perl and all the cached compiled code and persistent variables, this can be a great deal of memory — far more than you get with more ordinary Apache usage. Likewise, tuning MaxClients to avoid swapping can improve the performance even though, paradoxically, it actually causes people to have to wait.