Can someone describe in 30 words what ARCHIVEMODE is for?
I found this: 'When you enable this mode redo logs will be archived instead of overwritten.'
but have no idea, what can I write more about it.
If a database is in log archive mode, the database makes sure that online redo logs are not overwritten before they have been archived to a designated location. Typically there are more than two online redo logs in rotation within a database environment. If you have a DB file corruption and the transaction is not in your online redo logs, you lose that data. If you have your database in archive mode, then you may still recover using these offline (archived logs).
Archive logging is essential for production databases where the loss of any data might be fatal. It is generally considered unnecessary in development and test environments.