Forward Recovery (Redo):In this system the committed changes made by a transaction are reapplied to a previous copy of the database.
In simpler words, when a definite error in a system is detected, the recovery system creates an accurate assessment of the state of the system and then creates the appropriate adjustment based on the anticipated results - had the system been error free.
One thing to be well-known is that the Undo and Redo operations must be idempotent, i.e., implementing them several times must be equivalent to implementing them once. This characteristic is needed to guarantee correct behaviour of database even if a failure happens during the recovery process.
Depending on the above discussed recovery system; various types of recovery methods have been used. Though, we define the most important recovery schemes used in most of the commercial DBMSs.