CodeIgniter 2.1 Native PHP session library Plug'n'Play
Usage:
add to autoload in config\autoload.php:
$autoload['libraries'] = array('nativesession', 'other library', 'etc...');
OR
load dynamicaly in code:
$this->load->library('nativesession');
If you want to replace CodeIgniter Session library in existing code, load dynamicaly:
$this->load->library('nativesession', '', 'session');
And it should work without any major changes in your code.