ci_session with multiple database not working

I am working on a project where using two databases. My requirement is that, Depending on user login type load database e.g.

For user type 1 load db1(default database) Or For user type 2 load db2. Problem is that if login with user type 1 then logged in successfully but if login with user type 2 then login failed due to the ci_session table. how to fix this issue.