I am using two database one is default which I would like to set db name as per session value, second database I am using to login and registration and set session once user logged in.

Can anyone have solution to manage this database name after login of user based on session value..

I am using codeigniter framework

To proceed you'll have to share your code and hope folk will see where the issue is. This has many prior solved discussions with more than a few ways to do this. As such and because your system is your system there is no set piece of code you just slap into place.