What is the RESETLOGS option?

What is the RESETLOGS option?

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The RESETLOGS option is a method for opening a database, which results in a new database incarnation, the resetting of the log sequence number to 1, and the re-formatting or re-creation of the online redo logs.

An incomplete recovery of a database or a recovery using a backup control file requires the database to be opened with the RESETLOGS option (by using the ALTER DATABASE OPEN RESETLOGS; statement). RESETLOGS SCN, together with the RESETLOGS time stamp, uniquely identifies each execution of an ALTER DATABASE OPEN RESETLOGS; statement. The RESETLOGS SCN and time stamp are stored in the control file, data files' headers, online redo log files' headers, and archived redo log files' headers.

After a database is opened using the RESETLOGS option, all the archived redo logs become obsolete, as they can never be reapplied because the RESETLOGS SCN and time stamp stored in the archived redo logs become different from the RESETLOGS SCN and time stamp stored in the current control file. This prevents the data files from being corrupted due to the application of incorrect archived redo logs in the future.

In an incomplete recovery, all data files (except data files in an offline normal or read-only tablespace) must be recovered simultaneously. It is not possible to recover some data files at one time and the remaining data files later. This is because once the database is opened with the RESETLOGS option, the archived redo logs become obsolete and unusable for the recovery of the remaining data files. However, data files in an offline normal or read-only tablespace can be brought online even after opening the database with the RESETLOGS option. This is because they do not need the application of redo data.

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