Rolling Back and Roll forward Database Recovery.

Database can fail due to some reasons like media failure, operating system failure, accidental damage, and intentional damage to the database. When database stops working due to any above reasons, it's the responsibility of Database Administrator to recover the database using its backup files and restoration of database into the state it was in, before its failure. Normally full backup are done after one week but incremental backup are done on daily basis.

In these days, almost every database management system gives a number of methods to restore the failure database using its backup. It depends upon the size of backup file, when the size of database is large, recovery process may take a lot of time. There are two major types of complete recovery the database.

Backward Recovery

In backward Recovery the database is restored into the previous state and the unwanted changes are eliminated. It means that all changes made by various transactions are undone. For example, it will be equivalent to the state that was fifteen days before the failure. This sort of recovery is made when up to the time backup is not available or changes of previous period are needed to be undone.

Forward Recovery

It is also called Roll-forward. Changes of some failed transactions are applied to the database in order to roll it forward. Thus database becomes updated with all the changes confirmed.