Session data removed or overwritten

This conundrum was resolved by the answer to a separate topic (thanks Narf):
http://forum.codeigniter.com/thread-6400...#pid327251

In brief: If you have a db error which results in a rollback then any session data that you set in that context will also be rolled back. The alternative, if you need to set session data, is to use manual transactions so that you can roll back explicitly and then set your session data.

... or use MyISAM for the sessions table, because it doesn't support transactions.

Or use another session driver, like files. Seriously, unless your application directly accesses the sessions table, there's no advantage whatsoever to using the database driver.