It is not a bug in your application, it is only a missing driver, so, you have a couple of options.
Head over to your PHP init and then you uncomment the below code:
If not, do try installing it at your server, it varies depending on your distribution.
Try installing php5-mysqlnd.
If you can't do it by hosting restrictions then simply move to MySQL driver (won't have to change the other configurations or queries in the CodeIgniter or anything else...)
Like this (at your config file)
$db['default']['dbdriver'] = 'mysql'; (you might have mysqli now)
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