Codeigniter error: Call to undefined function mysql_pconnect()
<p>I have updated my codeigniter version from 2.2.4 step by step to 3.0.6 and I get an error:</p>

<pre><code>An uncaught Exception was encountered

Type: Error

Message: Call to undefined function mysql_pconnect()

Filename: path-to-project\system\database\drivers\mysql\mysql_driver.php

Line Number: 135

Backtrace:

File: path-to-project\application\controllers\Main.php
Line: 10
Function: __construct

File: path-to-project\index.php
Line: 315
Function: require_once
</code></pre>

<p>I have just replaced my index.php file and system directory with the new one and made some changes in my application according to tutorial. </p>

<p>and this is the Main controller:</p>

<pre><code>class Main extends CI_Controller {

    function __construct()
    {
        parent::__construct();
        $this-&gt;load-&gt;model('main_model');
    }
}
</code></pre>

<p>What causes the problem?!</p>

<p>And <a href="http://www.codeigniter.com/user_guide/installation/upgrade_300.html?highlight=upgrade" rel="noreferrer">this is the link</a> of the tutorial.</p>