When undo tablepsace is lost

Question

What happens when undo tablespace is lost and then instance aborted? How does roll back phase of crash recovery will be performed? what is your logic?
In my views, after restoring the undo tablespace, recovery will be performed. Since changes written to undo tablepsace always get recorded in redo log every time like any other datafile. Then during recovery, redo may applied to the undo tablespace, which helps in performing roll back phase of instance recoevry. Am I correct? If not, pls correct me.
Thnxs in advance.

Answer 1

As long as you can restore the Undo tablespace datafile(s) from a Backup, you can RECOVER the database.
In that respect, the Undo tablespace is no different from any other tablespace.
At the roll-forward stage, Oracle reads the archived redo and online redo and applies all changes to datafiles -- including undo datafiles.
At the OPEN stage, Oracle does a rollback of uncommitted transactions -- here it has to be able to read the Undo datafiles. So it needs the undo datafiles to be restored and recovered right upto the database's recovery point in time or upto complete recovery (which is the case when only the undo datafile has to be restored).
Hemant K Chitale