Alter database question ???

[anuragmin]

HI,
What does this command do

ALTER DATABASE CLEAR LOGFILE GROUP1 UNRECOVERABLE DATAFILE ;

Thanks
Anurag

[sambavan]

Hope this would help you.


To clear an inactive, online redo log group that has not been archived:

Clearing an unarchived log allows it to be reused without archiving it. This action makes backups unusable if they were started before the last change in the log, unless the file was taken
offline prior to the first change in the log. Hence, if you need the cleared log file for recovery of a backup, you cannot recover that backup.

1.If the database is shut down, then start a new instance and mount the database, but do not open it:

STARTUP MOUNT



2.Clear the log using the UNARCHIVED keyword. For example, to clear log group 2, issue:

ALTER DATABASE CLEAR LOGFILE UNARCHIVED GROUP 2;



If there is an offline datafile that requires the cleared unarchived log to bring it online, then the keywords UNRECOVERABLE DATAFILE are required. The datafile and its entire tablespace have to be dropped because the redo necessary to bring it online is being cleared, and there is no copy of it. For example, enter:

ALTER DATABASE CLEAR LOGFILE UNARCHIVED GROUP 2 UNRECOVERABLE DATAFILE;



3.Immediately back up the database using an operating system utility. Now you can use this backup for complete recovery without relying on the cleared log group. For example,
enter:

% cp /disk1/oracle/dbs/*.f /disk2/backup


4.Back up the database's control file using the ALTER DATABASE statement. For example, enter:

ALTER DATABASE BACKUP CONTROLFILE TO '/oracle/dbs/cf_backup.f';


Sam

[anuragmin]

Originally posted by sambavan
The datafile and its entire tablespace have to be dropped because the redo necessary to bring it online is being cleared, and there is no copy of it.
Sam

What happens under the follwoing scenario

1.Full Database backup taken at point A
2.Redo log 1a starts logging changes at point B
3.datafile 1 and unarchived redo log file 1a get corrupted at point C

How do I recover the database till the point of failure.
Will I need to use the command
ALTER DATABASE CLEAR LOGFILE UNARCHIVED GROUP 2 UNRECOVERABLE DATAFILE;

Does your above statement mean that I can only recover my database till point B.
what are the steps that need to be performed to recover such kind of a situation.

Thanks
Anurag

[Edited by anuragmin on 05-18-2001 at 05:46 PM]

[sambavan]

Go through this documentation and it talks about different scanarios.

http://technet.oracle.com/doc/oracle...a76993/toc.htm


Check chapter 6 and 7 for more details.

Sam