Performing Oracle User-Managed Database Recoveries - OCP: Oracle Database 12c Administrator Certified Professional - page 63

The recovery for each of these types of data file losses is similar. Some recoveries can be
done online (with the database up and running) and other recoveries will require that the
database be shut down (though in these cases it's likely going to have crashed anyway). We
will cover each of these types of loss in the following sections.
Restoring Data Files after the Loss of All Data Files
If you have lost all of your database data files, then you will need to perform a database
recovery with the database down. It is most likely in these cases that the database will have
already crashed anyway (or refused to restart); Oracle does not do well if all of the database
data files go missing.
The procedure in this case is simple:
1. Restore the data file backups from your backup media.
You can restore these data files to their original locations or to new locations depending
on your needs.
2. Once you have restored the data files, you are ready to recover the entire database.
We discuss full database recovery in the section “Recovering the Database” (an original
title, we know).
Restoring Data Files after the Loss of the SYSTEM or UNDO
Tablespace Data File
If you have lost only data files related to the SYSTEM or UNDO tablespace, then you should
restore only those data files. You will still need to do an offline recovery, but the recovery
will be much quicker since all you will need to do is recover those database data files. Once
you have recovered the data files from your backup media, perform a tablespace- or data
file-level recovery, which is covered in the section “Recovering the Database.”
Specific Recovery Actions
The OCP exam expects you to answer a question with the best answer. For example, in
the case of the loss of a single, non- SYSTEM or - UNDO tablespace data file, the best answer
is to restore just that data file and not all database data files Sure you can restore all the
data files, but that would not be the best course of action.
Restoring Data Files after the Loss of One or More Non-SYSTEM
or -UNDO Tablespace Data Files
If you lose a data file related to a tablespace other than the SYSTEM or UNDO tablespace, then
you can actually perform online recovery of the database. In these cases, it is unlikely that
the database will crash, and if the database is started up, it will seem to start up normally,