Whenever you open the database with the RESETLOGS option, all datafiles get a new RESETLOGS SCN and timestamp. Archived redo logs also have these two values in their header. Because Oracle will not apply an archived redo log to a datafile unless the RESETLOGS SCN and timestamps match, the RESETLOGS operations prevents you from corrupting your datafiles with old archived logs.

The RESETLOGS option is required after incomplete media recovery or recovery using a backup control file. Resetting the redo log:

• Discards any redo information that was not applied during recovery, ensuring that it will never be applied.
• Re-initializes the control file information about online redo logs and redo threads.
• Clears the contents of the online redo logs.
• Creates the online redo log files if they do not currently exist.
• Resets the log sequence number to 1.

A RESETLOGS operation invalidates all redo in the online logs. Restoring from a whole database backup and then resetting the log discards all changes to the database made from the time the backup was taken to the time of the failure.

In general, backups made before a RESETLOGS operation are not allowed in the new incarnation. There is, however, an exception to the rule: you can restore a pre-RESETLOGS backup only if Oracle does not need to access archived redo logs from before the RESETLOGS to perform recovery.

ALTER DATABASE OPEN RESETLOGS;