RubyOnRails : read parameter from the database once

How does this happen in RubyOnRails:
The parameter is stored in the database.
The program needs to read it from the database once upon user login and save them in a global variable.
While the user is working, he uses only this variable, and the program does not read parameter again from the DB, only the next time the user logs on to the system.
How it is implemented.