Oracle Backup & Recovery Techniques - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 325

Flashback Database

Once this feature is activated, the entire database can be taken to
a state back to any specific point in time and RVWR background
process gets live to write Flashback Database logs. Flashback
database logs contain the before image of physical database
blocks.

The Flashback Recovery Area must be enabled for the Flashback
database logs to be written.

How to activate Flashback Database feature?

The database has to be in the mounted state before enabling this
feature.

Step 1:
Run SQL*Plus and connect as SYSDBA.

C:\Documents and Settings\Administrator> SQLPLUS /NOLOG
SQL> CONNECT / AS SYSDBA

Step 2:
The following command will start the Oracle Instance and mount
the database.

SQL> STARTUP MOUNT

Step 3:
The following statement will set the

DB_FLASHBACK_RETENTION_TARGET initialization

parameter to two days. The value is in minutes.

SQL> ALTER SYSTEM SET
DB_FLASHBACK_RETENTION_TARGET = 2880;