This is something new I learned today from a DBA at Boeing.
Empty pot is easy to fill. "Stay hungry".
Those days many site only do online hot backup.
But cold backup still have it's suited scenario, e.g. backup dev db and clone.
Here is the script many people used to do.
The problem is when there are some long running active transactions, database instance will wait and not be closed.
Here is the workaround, force disconnect all active sessions, startup in a consistent state, and then close.
ALTER SYSTEM CHECKPOINT; -- I think this is optional. :)
Notes: This method is not recommended for production database.