Novell LINUX ENTERPRISE SERVER 11 - ADMINISTRATION Administration Manual page 410

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 being unable to communi-
cate with system resources. Another argument against using the worker MPM with
Apache is that not all available Apache modules are thread-safe and thus cannot be
used in conjunction with the worker MPM.
WARNING: Using PHP Modules with MPMs
Not all available PHP modules are thread-safe. Using the worker MPM with
mod_php is strongly discouraged.
27.4.5 External Modules
Find a list of all external modules shipped with SUSE Linux Enterprise Server here.
Find the module's documentation in the listed directory.
mod-apparmor
Adds support to Apache to provide Novell AppArmor confinement to individual
CGI scripts handled by modules like mod_php5 and mod_perl.
396 Administration Guide