Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual page 786

mod_userdir
Enables user-specific directories available under ~user/. The UserDir directive
must be specified in the configuration. This module is enabled by default.
40.4.4 Multiprocessing Modules
SUSE Linux Enterprise Server provides two different multiprocessing modules (MPMs)
for use with Apache.
Prefork MPM
The prefork MPM implements a nonthreaded, preforking Web server. It makes the Web
server behave similarly to Apache version 1.x in that it isolates each request and handles
it by forking a separate child process. Thus problematic requests cannot affect others,
avoiding a lockup of the Web server.
While providing stability with this process-based approach, the prefork MPM consumes
more system resources than its counterpart, the worker MPM. The prefork MPM is
considered the default MPM for Unix-based operating systems.
IMPORTANT: MPMs in This Document
This document assumes Apache is used with the prefork MPM.
Worker MPM
The worker MPM provides a multithreaded Web server. A thread is a "lighter" form
of a process. The advantage of a thread over a process is its lower resource consumption.
Instead of only forking child processes, the worker MPM serves requests by using
threads with server processes. The preforked child processes are multithreaded. This
approach makes Apache perform better by consuming fewer system resources than the
prefork MPM.
One major disadvantage is the stability of the worker MPM: if a thread becomes corrupt,
all threads of a process can be affected. In the worst case, this may result in a server
crash. Especially when using the Common Gateway Interface (CGI) with Apache under
heavy load, internal server errors might occur due to threads unable to communicate
with system resources. Another argument against using the worker MPM with Apache
768 Installation and Administration