What is the meaning of Recovery?

In deferred update methods, if a transaction fails before arriving its commit point, it will not have altered the database in any way, so UNDO is not required. Deferred update can lead to a recovery algorithm termed as NO-UNDO/REDO. This approach, while used with certain concurrency control methods, is designed never to need transaction rollback, and recovery simply contain redoing the operations of transactions committed after the last checkpoint from the log. In immediate update method, if a transaction fails after recording a few changes in the database but before reaching its commit point, the effect of its operations on the database should be undone; that is, the transaction should be rolled back. This technique needs both operations and is utilized most often in practice. Hence, it is as well known as UNDO/REDO.