Sessions may be deleted before the time limit you set in gc_maxlifetime.
If you have multiple pages on the same server, each using the session (the same or distinct named sessions, it doesn't matter), the *minimum* gc_maxlifetime of any of those scripts ends up being the effective lifetime of the session files.
This can also apply to the lifetime coming from a CLI invocation of a PHP script on that machine which happens to use the session.
This can be bothersome since even though you think all your pages include the same file which sets up the script, even a single PHP page which doesn't can invoke the GC and have the scripts deleted.
Thus, if you need to set a long gc_maxlifetime you are best doing this through the INI file or in a .htaccess file for the entire directory.
