codeigniter upgrade issue

My site is using codeigniter 2.1, I am upgrading to codeigniter 3.1.9, while upgrading search with pagination is not working. I changed the system/libraries/pagination.php from codeigniter 3.1 to 2.1 file, then It is working properly .In my search with pagination, we are using hidden value post data's not session, Can anyone please suggest solution for this issue?