Zkuste nastavit,
Další informace:https://www.codeigniter.com/user_guide/database/configuration. html
UPRAVIT: Zkuste tuto konfiguraci pro PDO
v postgres
$db['default']['hostname'] = 'pgsql:host=localhost;dbname=yourdb'; //set host
$db['default']['username'] = 'your username'; //set username
$db['default']['password'] = 'your password'; //set password
$db['default']['database'] = 'your database'; //set databse
$db['default']['dbdriver'] = 'pdo'; //set driver here