TIP #26 : UNDO tablespace recovery.

Here is handy steps for any UNDO tablespace issue.
Some example are :

• undo tablespace was dropped
• undo was not recreated
• undo was recreated without specifying 'undo' keyword.
  

To resolve the issue, Follow the following steps :

1. set undo_management to MANUAL
2. startup pfile
3. drop undo tablespace (If it was created wrongly without undo keyword)
4. create undo tablespace undotbs datafile '??????' size 1M reuse;
5. shutdown database.
6. set undo_management to AUTO-
7. startup