Consider two statements about database transaction schedules: I. Strict two-phase locking protocol g

Q: What is GATE-CS?

GATE-CS is a competitive examination conducted in India. This question is from the 2019 GATE-CS Database Management Systems paper.

Q: How can I prepare for GATE-CS Database Management Systems?

To prepare for GATE-CS Database Management Systems, practice previous year questions (PYQs), understand concepts thoroughly, and solve mock tests regularly. This 2019 question covers Transactions and Concurrency Control topic.

Q: What is the difficulty level of this question?

This GATE-CS 2019 Database Management Systems question has a hard difficulty level and is marked as an important question.

Q: Where can I find more GATE-CS previous year questions?

You can find more GATE-CS previous year questions on AspirantMitraa. Browse by subject, topic, year, and difficulty level to practice effectively.

Question

Consider 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 with Thomas' Write Rule can generate view serializable schedules that are not conflict serializable. Which are TRUE?

Accepted Answer

Correct Answer: (C) Both I and IIConcept: Concurrency Control ProtocolsStatement I — TRUE: Strict Two-Phase Locking (Strict 2PL) is a variant of 2PL where a transaction holds all its locks until it commits or aborts. All 2PL schedules are conflict serializable (this is the correctness guarantee of 2PL). Additionally, strict 2PL ensures recoverability: since write locks are held until commit, no other transaction can read uncommitted data written by this transaction, preventing cascading aborts. Strict 2PL also guarantees strict schedules, a stronger property than recoverability.Statement II — TRUE: The Timestamp Ordering protocol with Thomas' Write Rule modifies the basic timestamp protocol to allow certain late write operations (those that would have been rejected) to be silently ignored rather than causing a rollback. This optimization allows some non-conflict-serializable schedules to be accepted, but these schedules are still view serializable. View serializability is a strictly weaker condition than conflict serializability — all conflict-serializable schedules are view serializable, but not vice versa. Thomas' Write Rule exploits this gap.Definition: Conflict serializability means the schedule can be transformed into a serial schedule by swapping non-conflicting operations. View serializability is a broader condition requiring only that reads and writes see the same data values as some serial schedule.

Master GATE-CS with Our Test Series

More Questions from Transactions and Concurrency Control

Frequently Asked Questions

Master GATE-CS with Our Test Series

More Questions from Transactions and Concurrency Control

Frequently Asked Questions