Restore the undo file lost when the Oracle database is shut down normally

When the Oracle database is shut down normally, the committed transaction has been written into the data file, and the uncommitted transaction has been rolled back, the data in the control file, log file, and data file is consistent. You do not need to use the rollback information in the undo data file when you start the instance again.

An error is reported during normal startup. the recovery procedure is as follows:

1. log on to the system as an oracle user, sqlplus/as sysdba;
2. start mount;
3. alter database datafile '/u01/app/oracle/oradata/orcl/undotbs01.dbf' offline drop;
4. alter database open;
5. create undo tablespace undotbs2 datafile '/u01/app/oracle/oradata/orcl/undotbs02.dbf' size 200 m autoextend on maxsize 10g;
6. alter system set undo_tablespace = undotbs2;
7. drop tablespace undotbs1 including contents and datafiles;