This article is still under construction........

 Let's have a look at different points:

• Apache with PHP module consumes a lot of memory because each request is handled by one process.
• The worker MPM uses a thread based architecture as opposed to the pre-fork MPM which uses a process based architecture; the architectural differences between the two Multi-Processing Modules means that the worker MPM has a lower memory footprint.
• The pool of fcgid-invoked programs is shared between all httpd workers.
•  

 Related links.

The Status module allows a server administrator to find out how well their server is performing.

This module is normaly enable by default on ubuntu.

On a ubuntu distribution, you can edit the file
etc/apache2/mods-available/status.conf
for your personal configuration; for example to allow only from your ip.

Complete description can be found at apache website.