OCP 1Z0 053 178

178.If a log file becomes corrupted, it may cause the database to stall. How would you correct such a 
situation? 
A. Recover the online redo log from backup. 
B. Delete and re-create the log file. 
C. Use the alter database clear logfile command to clear the log file. 
D. Shut down the database and restart it. 
E. Shut down the database and then mount it. Clear the log file with the alter database clear logfile 
command and then restart the database with alter database open resetlogs. 
Answer: C 
 

online redo log在备份里是没有的。

如果损坏了，表示你的数据永远丢了。

clear它，然后RESETLOGS 启动吧

http://docs.oracle.com/cd/E11882_01/server.112/e25494/onlineredo.htm#ADMIN11327

Clearing a Redo Log File

A redo log file might become corrupted while the database is open, and ultimately stop database activity because archiving cannot continue. In this situation the ALTER DATABASE CLEAR LOGFILE statement can be used to reinitialize the file without shutting down the database.

The following statement clears the log files in redo log group number 3:

ALTER DATABASE CLEAR LOGFILE GROUP 3;

This statement overcomes two situations where dropping redo logs is not possible:

• If there are only two log groups

• The corrupt redo log file belongs to the current group

If the corrupt redo log file has not been archived, use the UNARCHIVED keyword in the statement.

ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 3;

This statement clears the corrupted redo logs and avoids archiving them. The cleared redo logs are available for use even though they were not archived.

If you clear a log file that is needed for recovery of a backup, then you can no longer recover from that backup. The database writes a message in the alert log describing the backups from which you cannot recover.

Note:

If you clear an unarchived redo log file, you should make another backup of the database.