Express Learning: Database Management Systems

10

Concurrency Control Techniques

1.   What is concurrency control? How is it implemented?

Ans: When several transactions execute concurrently, they may result in interleaved operations, and the isolation property of transaction may no longer be preserved. Thus, it may leave the database in an inconsistent state. To understand, consider a situation in which two transactions concurrently access the same data item. One transaction modifies a tuple, and the other makes a decision on the basis of that modification. Now, suppose that the first transaction rolls back. At this point, the decision of the second transaction becomes invalid. Thus, there is a need to control the interaction among concurrent transactions, which is referred to as concurrency ...