Which of the following statements about the Two Phase Locking (2PL) protocol is/are TRUE?
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GATE CSE 2024 Set 2 · Q27
MSQ1 markEasy
Time
Which of the following statements about the Two Phase Locking (2PL) protocol is/are TRUE?
Select all that applyOne or more correct
Pick every correct option
Solution
Step-by-step verified solution
Official 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
Transactions and Concurrency ControlLet us analyze each statement about the Two Phase Locking (2PL) protocol:
Statement (A) is TRUE: The 2PL protocol guarantees conflict serializability, ensuring that every schedule generated under 2PL is serializable.
Statement (B) is FALSE: Locking right before and unlocking right after each operation does not enforce two phases and can lead to non-serializable schedules. Under 2PL, locks are held across operations in a growing phase and cannot be released until the shrinking phase begins.
Statement (C) is TRUE: The fundamental rule of 2PL is that once a transaction enters the shrinking phase (i.e., releases its first lock), it can never acquire any further locks.
Statement (D) is TRUE: Basic 2PL is susceptible to deadlocks because transactions may hold locks and wait indefinitely for locks held by other transactions.
Hence, statements (A), (C), and (D) are TRUE.
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Examiner trap
The misconception this question tests
Recall the two distinct phases of 2PL (growing and shrinking) and its properties regarding serializability and deadlocks.
This Transactions and Concurrency Control previous year question is Q27 of the GATE CSE 2024 Set 2 paper. Find more GATE CSE PYQs on Transactions and Concurrency Control in Databases, or browse all GATE CSE PYQs.
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Transactions and Concurrency Control in GATE CSE
Transactions and Concurrency Control has 25 GATE CSE PYQs across 20 papers from 2012 to 2026. 3 of them are 1-mark MSQs like this one, and GATE CSE 2024 Set 2 has 2.
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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.