I want to create a thread that was started with rails server start up. This
Thread does some database update every day (automatically).
Sb knows where can I find some materials about it?
It would be impossible to suggest anything without knowing more about
your environment (at least, which OS).
For instance, you might achieve what you want with cron, or scheduled tasks.
Really? If you insist. But it seems like overkill to add scheduling to
your application for the requirement you described. But that's a
decision that only you can make.
That way the crons can also be maintained when you use capistrano and
they will be deployed to new machines if needed. It makes a great deal
of sense to bundle the application specific crons with he application
itself.