Question

Which of the following concurrency control protocols ensure both conflict serializability and freedom from deadlock?

I. 2-phase locking

II. Time-stamp ordering

1. I only
2. II only
3. Both I and II
4. Neither I nor II

Answer 1

Correct Answer - Option 2 : II only

• 2 PL is based on locks and hence not free from deadlock but ensures conflict serializability.
• Timestamp ordering protocol is based on timestamps ensures conflict serializability and is also free from deadlock.

Hence the correct answer is II only.

•  Any schedule is possible under 2PL it must ensure conflict serializability.
• Deadlock may occur under 2PL.
• Cascading rollbacks may occur under 2PL.