Server-Pool Size Regulation

When the Apache HTTP Server accepts requests, it dispatches child processes or threads to handle them. This group of child processes or threads is known as a server-pool. Under Apache HTTP Server 2.0, the responsibility for creating and maintaining these server-pools has been abstracted to a group of modules called Multi-Processing Modules (MPMs). Unlike other modules, only one module from the MPM group can be loaded by the Apache HTTP Server. There are three MPM modules that ship with 2.0: prefork, worker, and perchild. Currently only the prefork and worker MPMs are available, although the perchild MPM may be available at a later date.

The original Apache HTTP Server 1.3 behavior has been moved into the prefork MPM. The prefork MPM accepts the same directives as Apache HTTP Server 1.3, so the following directives may be migrated directly:

The worker MPM implements a multi-process, multi-threaded server providing greater scalability. When using this MPM, requests are handled by threads, conserving system resources and allowing large numbers of requests to be served efficiently. Although some of the directives accepted by the worker MPM are the same as those accepted by the prefork MPM, the values for those directives should not be transferred directly from an Apache HTTP Server 1.3 installation. It is best to instead use the default values as a guide, then experiment to determine what values work best.

To use the worker MPM, create the file /etc/sysconfig/httpd and add the following directive: 

HTTPD=/usr/sbin/httpd.worker

For more on the topic of MPMs, refer to the following documentation on the Apache Software Foundation's website: