During the Magento installation you’re given the option whether you want to save session data in the database or in the filesystem. Generally, saving the session information in the database is the better option for larger sites, as this allows easier clustering for multiple servers. For smaller websites you might want to save the extra queries and just go with saving the session data in the filesystem, although this could be a bit slower. If you ever want to switch between the two options just follow the following steps.
FTP into your Magento installation and open ‘app/etc/local.xml’. Look for the line that starts with ‘<session_save>’ and replace it with either of the two options below.
// For storing session data in the database use this line. <session_save><![CDATA[db]]></session_save> // For storing session data in the filesystem use this line. <session_save><![CDATA[files]]></session_save>
After saving the file remove all files and folders in the ‘var/session’ and ‘var/cache’ folders.