• Oracle stores these flashback logs in the flashback recovery area.

• If you want to flashback to 8:00 A.M., it may turn out that the flashback logs nearest to   the target time were written at 7:56 A.M. To cover this gap, you must apply the changes   from archived or online redo log files pertaining to that period.

• Always remember that Oracle doesn’t guarantee that you can flashback your database   to the flashback retention target. If Oracle is running low on free space in the flash   recovery area for newly arriving archived redo log files, it will remove some flashback   logs to make room.

• If a datafile was resized during the time span covered by the Flashback Database operation, you can’t flashback that datafile. Instead, you must offline that particular datafile before you start the flashback database operation.

• If a control file has been restored or re-created during the time span you want to   flashback over, you can’t use the Flashback Database feature.

• You can’t flashback a database to before a RESETLOGS operation.

• You can’t flashback a datafile that was dropped or shrunk during the time span covered   by the flashback table operation.

1. Ensure that your database is in the archivelog mode.

2. Your database must be using the flash recovery area.

3. You must set the initialization parameter DB_FLASHBACK_RETENTION_TARGET to set your flashback retention target (in minutes).

4. Shut down the database and restart in the MOUNT EXCLUSIVE mode.

5. Turn the flashback database feature on with the following command:

6. Use the ALTER DATABASE OPEN command to open the database.

Note: You can turn the feature off by using the ALTER DATABASE FLASHBACK OFF command while the database in the MOUNT EXCLUSIVE mode. When you do so, Oracle deletes all flashback database logs in the flash recovery area.

Note: If you don’t want certain tablespaces to be part of your flashback operations, issue the following command after setting the tablespace offline:

1. Restart the database in the MOUNT (exclusive) mode then issue one of the commands:

2. Open the database with READ ONLY option to check that the database flashed back to the correct time.

3. If you decide to go back further in time, you can flashback the database again.

4. If you determine that you flashed back too far into the past, you can use redo logs to roll forward.

5. Open the database with RESETLOGS option:

6. If you want to completely undo the effects of the flashback database operation, just use the command RECOVER DATABASE to perform a complete recovery of the database.

In order to estimate the space you need to add to your flash recovery area for accommodating the flashback database logs:

To really know how far back you can flashback your database at any given time, you must query the V$FLASHBACK_DATABASE_LOG in the following manner:

The view V$FLASHBACK_DATABASE_STATS helps you monitor the I/O overhead of logging flashback data.

BEGIN_TIME and END_TIME - stands for the beginning and ending hourly time intervals for which the view’s statistics were collected. Oracle collects flashback data on an hourly basis for a maximum of 24 hours. If you issue a query on the table, however, it may return 25 rows, the 25th row being for the most recent fraction of time after the last (24th) row was logged in the view.

FLASHBACK_DATA - stands for the number of bytes of flashback data written during the interval.

DB_DATA - stands for the number of bytes of database data read and written during the interval.

REDO_DATA - stands for the number of bytes of redo data written during the interval.

ESTIMATED_FLASHBACK_SIZE - is identical to the value of the  ESTIMATED_FLASHBACK_SIZE column in the V$FLASHBACK_DATABASE_LOG view.