Control file change sequence number

After the database is opened, the datafile stop SCN in the control file once again changes to NULL to indicate that the datafile is open for normal use. SCN after an Instance Crash. The previous example showed the behavior of the SCN after a clean shutdown. This information enables Oracle, at the time of the next startup, to determine that the instance crashed because the checkpoint on shutdown was not performed.

If an instance crashes at shutdown, then instance crash recovery is required the next time the instance starts up. Recovery from an Instance Crash. Oracle then performs crash recovery. During crash recovery, Oracle applies redo log records from the online redo logs in a process referred to as roll forward to ensure that all transactions committed before the crash are applied to the datafiles. Following roll forward, active transactions that did not commit are identified from the rollback segments and are undone before the blocks involved in the active transactions can be accessed.

This process is referred to as roll back. After instance startup, the X table exists, but remains empty. Instance recovery happens automatically at database startup without database administrator DBA intervention. Recovery from a Media Failure. Up until this point, the checkpoint start SCN in the datafile header has always matched the datafile checkpoint SCN number held in the control file.

This is reasonable because during a checkpoint, the datafile checkpoint SCN in the control file and the start SCN in the datafile header are both updated, along with the system checkpoint SCN. At instance startup, the datafile checkpoint SCN in the control file and the start SCN in the datafile header are checked for equality. For example, media recovery is required if a media failure has occurred and the original datafile has been replaced with a backup copy.

In this case, the start SCN in the backup copy is less than the checkpoint SCN value in the control file, and Oracle requests archived redo logs—generated at the time of previous log switches—in order to reapply the changes required to bring the datafile up to the current point in time. Thank you! You really have a talent to explain difficult things easy. Because the RMAN configuration is back to the default we are going to have to pass the entire path along with the file name of the latest control file autobackup to the restore control file command.

We just restored the control files. Oracle embeds the DBID in the name of the control file autobackup.

In this case our control file autobackups were configured as shown below. The first number after the c-, , is the DBID. With the DBID set, we can now recover the control files from the control file autobackup.

Again we have to pass the entire path along with the control file auto backup name. I think after seeing what is required to restore the control files you will agree that multiplexing the control files is a good thing to do. You can say, go man check it in Oracle Documentation, yes you are right, but I would like to know your view and suggestions in handling the situation.

Just interest in DBs. This is really a awesome document. Thanks But the same doubt what if rman backup is not there. Assume you work in a company as a senior DBA and on your absence your buck up has corrupted all the control files while working with the alter dba backup control files command.

What would restore database and recover database command do. LOG References Etrack : Was this content helpful? Yes No Rating submitted. Please provide additional feedback optional :.

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