GATE CS 2019 Set 1 — Question 21

MCQ+1 / -0.33MediumConflict SerializabilityTransactions & ConcurrencyDatabasesView SerializabilityRecoverabilityTwo-Phase LockingTimestamp Protocols

Databases → Transactions & Concurrency → Conflict Serializability

Last updated 5 September 2026

Question

Consider the following two statements about database transaction schedules: I. Strict two-phase locking protocol generates conflict serializable schedules that are also recoverable. II. Timestamp-ordering concurrency control protocol with Thomas' Write Rule can generate view serializable schedules that are not conflict serializable. Which of the above statements is/are TRUE?

Correct answer (C) Both I and II Solution Statement I is TRUE : Strict Two-Phase Locking (Strict 2PL) ensures that a transaction holds all its exclusive locks until it commits or aborts. This property guarantees that the schedule is strict (and thus recoverable and cascadeless). Since it follows 2PL, it also guarantees conflict serializability. Statement II is TRUE : Thomas' Write Rule is an optimization on the Timestamp Ordering protocol that ignores obsolete write operations (writes that arrive late). By ignoring these writes, it allows schedules that would otherwise be rejected by basic TO or conflict serializability checks. These schedules are view serializable but not necessarily conflict serializable. Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (C) Both I and II Solution Statement I is TRUE : Strict Two-Phase Locking (Strict 2PL) ensures that a transaction holds all its exclusive locks until it commits or aborts. This property guarantees that the schedule is strict (and thus recoverable and cascadeless). Since it follows 2PL, it also guarantees conflict serializability. Statement II is TRUE : Thomas' Write Rule is an optimization on the Timestamp Ordering protocol that ignores obsolete write operations (writes that arrive late). By ignoring these writes, it allows schedules that would otherwise be rejected by basic TO or conflict serializability checks. These schedules are view serializable but not necessarily conflict serializable.

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