Overview
An overview of PHP session management is shown in Figure 8-1. When a user first enters the session-based application by making a request to a page that starts a session, PHP generates a session ID and creates a file that stores the session-related variables. PHP sets a cookie to hold the session ID in the response the script generates. The browser then records the cookie and includes it in subsequent requests. In the example shown in Figure 8-1, the script welcome.php records session variables in the session store, and a request to next.php then has access to those variables because of the session ID.
Figure 8-1. The interaction between the browser and the server when initial requests are made to a session-based application
The out-of-the-box configuration of PHP session management uses disk-based files to store session variables. Using files as the session store is adequate for most applications in which the numbers of concurrent sessions are limited. A more scalable solution that uses a MySQL database as a session store is provided in Appendix D.