has halted, then perform one of procedures in this section, depending on the archiving mode.
The current log is the one LGWR is currently writing to. If a LGWR I/O operation fails, then LGWR terminates and the instance fails. In this case, you must restore a backup, perform incomplete recovery, and open the database with the RESETLOGS option.
Recovering from the Loss of Active Logs in NOARCHIVELOG Mode
In this scenario, the database archiving mode is NOARCHIVELOG.
To recover from the loss of an active online log group in NOARCHIVELOG mode:
If the media failure is temporary, then correct the problem so that the database can reuse the group when required.
Restore the database from a consistent, whole database backup (data files and control files). For example, enter:
% cp /disk2/backup/*.dbf $ORACLE_HOME/oradata/trgt/
Mount the database:
STARTUP MOUNT
Because online redo logs are not backed up, you cannot restore them with the data files and control files. To allow the database to reset the online redo logs, you must first mimic incomplete recovery:
RECOVER DATABASE UNTIL CANCEL
CANCEL
Open the database using the RESETLOGS option:
ALTER DATABASE OPEN RESETLOGS;
Shut down the database consistently. For example, enter:
SHUTDOWN IMMEDIATE
Make a whole database backup.
If the media failure is temporary, then correct the problem so that the database can reuse the group when required. If the media failure is not temporary, then use the following procedure.
Recovering from Loss of Active Logs in ARCHIVELOG Mode
In this scenario, the database archiving mode is ARCHIVELOG.
To recover from loss of an active online redo log group in ARCHIVELOG mode:
Begin incomplete media recovery, recovering up through the log before the damaged log.
Ensure that the current name of the lost redo log can be used for a newly created file. If not, then rename the members of the damaged online redo log group to a new location. For example, enter:
ALTER DATABASE RENAME FILE "/disk1/oradata/trgt/redo01.log" TO "/tmp/redo01.log";
ALTER DATABASE RENAME FILE "/disk1/oradata/trgt/redo02.log" TO "/tmp/redo02.log";
Open the database using the RESETLOGS option:
ALTER DATABASE OPEN RESETLOGS;
Note:
All updates executed from the end point of the incomplete recovery to the present must be re-executed.
Loss of Multiple Redo Log Groups
If you have lost multiple groups of the online redo log, then use the recovery method for the most difficult log to recover. The order of difficulty, from most difficult to least difficult, is as follows:
The current online redo log
An active online redo log
An unarchived online redo log
An inactive online redo log
来源： >