Curropt Undo tablespace

Question

Hi,
Was doing an exercise of bringing the database up if one of the datafile is curropt and the data on that data file is not required.
I did this:-
1. While the database is running I edited the datafile , dropped some junk in it.
2. Shutdown.
3. Startup mount
4. alter database datafile 'xxx' offline drop;
5. alter database open;
6. drop tablespace yyy.
7. create tablespace.
Worked ok.
But when I tried this for undo (just out of curiosity).
alter database datafile...
alter database open;
create undo tablspace new_undo;
alter system set undo_tablespae = new_undo;
drop old undo_tbs <<<< failed.
says active rollback segment exists.
Actually I tried this exercise twice first time I was able to drop the old undo tablespace but the second time it didn't.
Can somebody show how to open the database in this scenario i.e if the datafile asscoiated with undo tablespace is curropt.
Thanks.

Answer 1

Hi,
The size of the undo tablespace is related to the transaction activity and size and the setting of the undo_retention parameter.
You can use the undo advisor in OEM for setting an optimal value or size (see link).
http://www.oracle.com/technology/obe/10gr2_db_vmware/manage/undo/undoadv.htm#t4
Can you post the current size of thedatabase, the undo tablespace and the value of undo_retention?
Regards,
Tycho