Understanding Flashback Technology - OCP: Oracle Database 12c Administrator Certified Professional - page 386

One major technological benefit of Flashback Database is that it allows you to reverse user
errors or logical corruption much more quickly than performing a traditional incomplete
recovery or using the Oracle Log Miner utility. The reason Flashback Database recovery
is much quicker than traditional recovery operations is that recovery is no longer impacted
by the size of the database. The mean time to recovery (MTTR) for traditional recovery is
dependent on the size of the data files and archive logs that need to be restored and applied.
Using Flashback Database recovery, recovery time is proportional to the number of changes
that need to be backed out of the recovery process, not the size of data files and archive logs.
This makes the Flashback Database recovery process the most efficient recovery process in
most user-error or logical-corruption situations.
The Flashback Database architecture consists of the recovery writer RV W R background pro-
cess and Flashback Database logs. When the Flashback Database is enabled, the RVWR process
is started. Flashback Database logs are a new type of log file that contain a “before” image of
physical database blocks. The RVWR writes the Flashback Database logs in the fast recovery
area. Enabling the fast recovery area is a prerequisite to using Flashback Database because the
Flashback Database logs are written to the fast recovery area.
In the following sections, you will learn how to configure, monitor, and perform
Flashback Database operations.
Configuring Flashback Database
The database must have multiple features configured prior to configuring Flashback
Database. The database must have ARCHIVE LOG enabled. As mentioned earlier, the fast
recovery area must be configured to store the Flashback Database logs.
First, make sure the database is shut down. Next, the database must be started in mount
mode. Then, the database parameter DB_FLASHBACK_RETENTION_TARGET can be set to the
desired value, which is based on minutes. This value determines how far back in time you
can flash back the database. This is like a baseline for Flashback Database. Next, Flashback
Database can be enabled with the ALTER DATABASE FLASHBACK ON command. Finally, the
database can be opened for normal use.
Let's walk through these steps in more detail:
1. Start the database in mount mode:
SQL> connect / as sysdba
SQL> startup mount
ORACLE instance started.
Total System Global Area 535662592 bytes
Fixed Size 1334380 bytes
Variable Size 171967380 bytes
Database Buffers 356515840 bytes
Redo Buffers 5844992 bytes
Database mounted.