"This is the first article of several on developing an architecture for Enterprise PHP, where we are running dedicated PHP servers tuned to serve large number of web pages. This work originated in the need to save the current working database connection in a primary and fallback database server configuration. One of the most common feature requests that PHP developers ask for is application variables. These are variables that are globally available to all PHP scripts on a web server."

Application variables are nice when dealing with large systems, somewhat like the config files we see so often. The difference is that if the application variable $a is equal to 1, and a user increments that variable by 1, other users will have $a equal to 2.

This is a good tutorial on ways to setup application variables on your system.