From IBM developerWorks:

Applications using the LAMP (Linux®, Apache, MySQL, PHP/Perl) architecture are constantly being developed and deployed. But often the server administrator has little control over the application itself because it's written by someone else. This series of three articles discusses many of the server configuration items that can make or break an application's performance.

Tuning LAMP systems, Part 1: Understanding the LAMP architecture
Tuning LAMP systems, Part 2: Optimizing Apache and PHP
Tuning LAMP systems, Part 3: Tuning your MySQL server