Which of the following is correct ? I. Two phase locking is an optimistic…
2014
Which of the following is correct ?
I. Two phase locking is an optimistic protocol.
II. Two phase locking is pessimistic protocol
III. Time stamping is an optimistic protocol.
IV. Time stamping is pessimistic protocol.
- A.
I and III
- B.
II and IV
- C.
I and IV
- D.
II and III
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Correct answer: B
"Pessimistic" means the system assumes conflicts will happen and takes action early to prevent them.
Statement II: Two-Phase Locking is a pessimistic protocol.
It forces a transaction to acquire a lock before accessing data. If another transaction holds the lock, the current one must wait. This "lock-before-use" approach is the definition of pessimistic control.
Statement IV: Time stamping is a pessimistic protocol.
Even though it doesn't use locks, it is pessimistic because it decides the order of execution as soon as a transaction starts. If a transaction tries to access data in a way that violates its timestamp order, it is immediately aborted and restarted.
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