What exactly is the PHP function session_module_name for?

Question

PHP Session related functions have this one: session_module_name. The documentation only says:

session_module_name — Get and/or set the current session module

Nothing about what session modules are, what options available, and when it to use.

What is the purpose of this function?

Answer 1

The session_module_name defines how sessions are stored. You can use this in conjunction with session_set_save_handler to handle sessions manually, such as if you wanted to save/load sessions from a database. A quick search shows that there are at least 3 modules

<?php
  session_module_name("files");  // ASCII files
  session_module_name("mm");     // Shared memory
  session_module_name("user");   // Custom session backend
?>

Perhaps there are more. It would be nice if the session_module_name docs entry was a bit more helpful.