Enabling Flashback Database
Follow these are the steps to enable Flashback Database.
To enable flashback logging:
Ensure the database instance is open or mounted. If the instance is mounted, then the database must be shut down cleanly unless it is a physical standby database. Other Oracle RAC instances can be in any mode.
Optionally, set the DB_FLASHBACK_RETENTION_TARGET to the length of the desired flashback window in minutes:
ALTER SYSTEM SET DB_FLASHBACK_RETENTION_TARGET=4320; # 3 days
By default DB_FLASHBACK_RETENTION_TARGET is set to 1 day (1440 minutes).
Enable the Flashback Database feature for the whole database:
ALTER DATABASE FLASHBACK ON;
Optionally, disable flashback logging for specific tablespaces.
By default, flashback logs are generated for all permanent tablespaces. You can reduce overhead by disabling flashback logging for specific tablespaces as in the following example:
ALTER TABLESPACE tbs_3 FLASHBACK OFF;
You can re-enable flashback logging for a tablespace later with this command:
ALTER TABLESPACE tbs_3 FLASHBACK ON;
If you disable Flashback Database for a tablespace, then you must take its datafiles offline before running FLASHBACK DATABASE.
When you enable Flashback Database while the database is open, there is a very small chance the command may not be able to obtain the memory it needs. If the command fails because of that reason, retry the command after a while or retry after a shutdown and restart of the instance.
When you enable Flashback Database on a physical standby database, you can flash back a standby database. Flashback Database of standby databases has some applications in the Data Guard environment. See Oracle Data Guard Concepts and Administration for details.