GATE CS 2024 Set 2 — Question 27

MSQ+1 / -0MediumTwo-Phase LockingTransactions & ConcurrencyDatabases

Databases → Transactions & Concurrency → Two-Phase Locking

Last updated 20 August 2026

Question

Which of the following statements about the Two Phase Locking (2PL) protocol is/are TRUE?

Correct answer (A) 2PL permits only serializable schedules; (C) With 2PL, once a lock is released on any data item inside a transaction, no more locks on any data item can be obtained inside that transaction; (D) A deadlock is possible with 2PL Solution (A) TRUE : The Two Phase Locking (2PL) protocol guarantees conflict serializability. Any schedule allowed by 2PL is serializable. (B) FALSE : This statement describes a locking strategy that does not follow the two-phase rule. In 2PL, a transaction must acquire all necessary locks (Growing Phase) before it releases any lock. It cannot release a lock "just after the operation" if it intends to acquire more locks later. (C) TRUE : This is the definition of the Shrinking Phase in 2PL. Once a transaction releases a lock, it enters the shrinking phase and cannot acquire any new locks. (D) TRUE : 2PL does not prevent deadlocks. Transactions can wait for each other in a cycle (e.g., T1 holds A and waits for B, T2 holds B and waits for A) while adhering to 2PL rules. Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (A) 2PL permits only serializable schedules; (C) With 2PL, once a lock is released on any data item inside a transaction, no more locks on any data item can be obtained inside that transaction; (D) A deadlock is possible with 2PL Solution (A) TRUE : The Two Phase Locking (2PL) protocol guarantees conflict serializability. Any schedule allowed by 2PL is serializable. (B) FALSE : This statement describes a locking strategy that does not follow the two-phase rule. In 2PL, a transaction must acquire all necessary locks (Growing Phase) before it releases any lock. It cannot release a lock "just after the operation" if it intends to acquire more locks later. (C) TRUE : This is the definition of the Shrinking Phase in 2PL. Once a transaction releases a lock, it enters the shrinking phase and cannot acquire any new locks. (D) TRUE : 2PL does not prevent deadlocks. Transactions can wait for each other in a cycle (e.g., T1 holds A and waits for B, T2 holds B and waits for A) while adhering to 2PL rules.

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