How CodeIgniter close db connections?

There is a db->close() method. In a PHP environment that is not using persistent connections there is no real need to call it. For MySQL in particular, all open non-persistent MySQL connections and result sets are automatically destroyed when a PHP script finishes its execution. Which in CodeIgniter happens right after the controller method finishes. So you could call $this->db->close(); in some model or in a controller. But all you would accomplish is freeing up the connection resources a few microseconds earlier than if you let script execution finish.

If you have a high-demand situation and are therefore using persistent connections that is a different story. http://php.net/manual/en/features.persis...ctions.php