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Database Recovery System

1.   Define recovery manager. What are the properties of transactions that it preserves?

Ans: The component of DBMS that is responsible for performing the recovery operations is called recovery manager. The main aim of recovery is to restore the database to the most recent consistent state.

The recovery manager ensures that the two important properties of transactions namely, atomicity and durability are preserved. It preserves atomicity by undoing actions of uncommitted transactions and durability by ensuring that all the actions of committed transactions survive any type of failure.

2.   What information is maintained by recovery manager during normal execution of transactions?

Ans: The recovery manager maintains some information during normal execution of transactions to enable it to perform its task in the event of failure. When a DBMS is restarted after a crash, the control is given to the recovery manager, which is responsible to bring the database to a consistent state. It maintains a system log of all the modifications to the database and stores it on the stable storage, which is guaranteed to survive failures. The stable storage is implemented by storing the database on a number of separate non-volatile storage devices such as disks or tapes (perhaps in different locations). Information residing in stable storage is assumed to be never lost.