Explain Deadlock detection and recovery

Deadlock Detection - A deadlock is said to take place when there is a circular chain of transaction, every waiting for the release of a data - item held by the next transaction in the chain, the algorithm to detect a deadlock is relies on the detection of such type of a circular chain in the current system in wait - for - graph. The algorithm produces the wait - for - graph at regular intervals and observes it for a chain. The algorithm begins with the assumption that there is no deadlock. 

Deadlock Recovery - To recover from deadlock. The cycles in the wait - for - graph should be broken. The general method of doing this is to roll back one or much more transactions in the cycles till the system shows no further deadlock situation. The procedure of deadlock recovery must make sure that a given transaction is not constantly the one chosen for rollback. The selection of the transaction to be rolled back is relies on the following considerations: 

• The progress of the transaction and the number of data - items it has employed and modified.
• The amount of computing lasting for the transaction and the number of data - items that have yet to be accessed through the transaction.
• The relative cost of rolling back a transaction.