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

My application structure: 

• CI 3.1.4 with HMVC - All controllers/models/views are in modules
  
• "pconnect" is set to FALSE
  
• "mysql.allow_persistent = Off" is added to php.ini
  
• Module A is called for loading a page (an extensive form)
  
• Module A then calls Modules B to M for loading various (reusable) sections of the page (the form)
  
• Modules B to M may initiate connections to databases if needed (queries are not overly complex, though have a few cross-database joins)
  

Working perfectly on localhost. Gives following error on live server (shared hosting).

Message:  mysqli::real_connect(): (42000/1203): User <user> already has more than 'max_user_connections' active connections
Filename:mysqli/mysqli_driver.php
Line Number: 201

Now, will CI close database connections after finishing execution of Module A script or after finishing individual execution of Modules B to M scripts (which are actually creating database connections). Logically (and "intelligently"), it should be the latter.

The connections in cross-database joins within CI are not clear. How are they opened, managed, and closed? Can those connections cause "max_user_connections" error in MySQL on live server where allowed limit is 10-15?

Any help is appreciated. Thanks.