How are sessions stored?

The default behaviour for session storage is to save the session data in a file. This behaviour can be altered by changing the session.save_handler in your php.ini file. Options can be:

1. files
2. mm
3. database
4. SQLite

If we choose we can have this stored in one of the options above.

In files  session's are stored in /var/lib/php5 in Debian based linux
file is named like "sess_v93e2jhpjho4s4ea7r93vkbvu7" and data is stored like
foo|s:3:"bar";animals|a:8:{i:0;s:3:"cat";i:1;s:3:"dog";i:2;s:5:"mouse";i:3;s:4:"bird";i:4;s:9:"crocodile";i:5;s:6:"wombat";i:6;s:5:"koala";i:7;s:8:"kangaroo";}

The mm option saves the session data into memory, this also gives significant speed increase and is often recommended by tutorials for fine tuning PHP and apache web server.

Sessions may also be stored in a database. This option provides for greater manageability of sessions and allows the programmer to perform tasks such as counting of active sessions etc.In this session storage is permanent.

With the advent of PHP5, we now have SQLite bundled with PHP. If PHP is configured --with-sqlite, you will have access to saving sessions with a PHP native database, although SQLite is not truly a database, but a file abstraction layer with and SQL interface.