Flashback Database Vs. RMAN Recovery

1)  Flashback Database Vs. RMAN incomplete recovery
Flashing back a database to an earlier point in time yields a same result as an incomplete(Point-int-time) RMAN recovery would yield. But the difference is that Flashback Database uses the flashback logs stored in FRA and RMAN incomplete recovery uses a backup set and archived logs.

I was personally curious whether Flashing back a database is really faster than doing a incomplete RMAN recovery. Oracle says that it is. But I wanted to test myself. So I tested and found that it is true. I was even impressed with how quickly the testing flashback job was completed. I dropped a user(schema) in the testing database. The schema had a lot of data. Then I logged in the testing database through RMAN session and ran the flashback database command. It only took a few seconds.


2) When to use Flashback database?  When to use RMAN recovery?
Flashback technology seems to be very effective when we want to recover from some errors that has happened recently(not a few days ago or not a couple of weeks ago).  How far back can we flash back our database?  It depends on how long we keep our undo data(undo_retention) or our flashback logs (db_flashback_retention_target).  It seems that these two parameters are not normally set to a large number. They are probably set to a relatively smaller number with the consideration of disk space management. undo_retention is set to 15 minuites by default. And db_flashback_retention_target seems to be set to something like 48 hours according to Oracle's documentation in OTN.

So I would probably use RMAN Incomplete Recovery if I want to recover my database to a relatively more earlier point in time. (example:  5 days ago, 1 week ago, or 3 weeks ago)  Flashback database basically involves with rolling back our database incrementally to earlier point in time. Rolling back our database incrementally all the way back to the point in time 2 weeks ago or a month ago will probably takes much longer than restoring and recovering the database with a backupset and relatively a small set of archived logs.

In sum, I think that RMAN Backup/Recovery and Flashback technology are just complementary to making a proper and effective database recovery strategy. I guess that it is good to have both of them in place.


(3) How to configure/enable Flashback Database
- We need to first configure Fast Recovery Area(FRA) because the flashback logs are only stored in FRA.
- We also need to ensure that our database is running in Archivelog mode
- Set db_flashback_retention_target parameter.
    SQL> alter system set db_flashback_retention_target = 2880 scope=both;
- Open the database in MOUNT EXCLUSIVE mode.
- Alter database to Flashback ON
     SQL> alter database flashback ON;