Web Database Applications with PHP and MySQL, 2nd Edition

PHP Session Management

In Chapter 10, we described the three characteristics of session management: storing session variables, matching these session variables to HTTP requests using a session identifier, and removing timed-out sessions with garbage collection. PHP session management largely takes care of these issues, and with the default configuration, you needn't worry how storage, session identification, and garbage collection are performed.

To understand what we accomplish in this appendix, you should know a bit about what PHP does behind the scenes. You should also understand the layers within the PHP session support and how you can hook your own functions in.

Figure F-2 shows how session variables are stored and retrieved when PHP runs an application script that uses session support. PHP session support is divided into two layers: the PHP session management layer provides the interface to session-based scripts, and the storage layer is responsible for reading and writing session variables in the session store. The storage layer in the default configuration works with files in a directory designated for PHP session storage.

Figure F-2. PHP session management

When a script makes a call to session_start( ), the PHP session management layer reads the session ID from the HTTP request, starts a session by making open and read calls to the storage layer, and initializes the session variables ...