Since the database was shut down abnormally, the DBA tries to mount it. The DBA uses the startup open command to mount the database(1) and gets an error message showing what is wrong with the database. From the error message, the DBA knows that the online log #4 is corrupted(2)
The DBA queries the data dictionary view V$LOG to find information about the damaged online redo log. From the result, (4) the DBA knows that the online log #4 is not the current online redo log,
and that online log #4 is archived (5). The value zero for the FIRST_CHANGE column indicates that there is some problem with the
redo log file. The DBA concludes that no data is lost and, thus, no recovery is needed.
To correct the situation, the DBA needs to clear the corrupted online redo log and open the database.