Consider the following partial Schedule S involving two transactions T1 and T2. Only the read and the write operations have been shown. The read operation on data item P is denoted by read(P) and the write operation on data item P is denoted by write(P). Suppose that the transaction T1 fails immediately after time instance 9. Which one of the following statements is correct? A) T2 must be aborted and then both T1 and T2 must be re-started to ensure transaction atomicity B) Schedule S is non-recoverable and cannot ensure transaction atomicity C) Only T2 must be aborted and then re-started to ensure transaction atomicity D) Schedule S is recoverable and can ensure atomicity and nothing else needs to be done

Official answer: B) Schedule S is non-recoverable and cannot ensure transaction atomicity. Explanation: In the given schedule S: - At time instance 2, transaction T1 performs write(A). - At time instance 7, transaction T2 performs read(A), reading the uncommitted value written by T1. - At time instance 8, transaction T2 performs commit. A schedule is defined as recoverable if, whenever transaction Tj reads a value written by transaction Ti, the commit operation of Ti appears before the commit operation of Tj. Here, T2 reads from uncommitted transaction T1 and commits at time 8 while T1 has not yet committed. When T1 fails after time instance 9, it must be aborted and its updates rolled back to maintain atomicity. However, because T2 has already committed (durability), its actions cannot be undone (cannot be rolled back). Therefore, Schedule S is non-recoverable and cannot ensure transaction atomicity. Hence, option (B) is correct.

A) T2 must be aborted and then both T1 and T2 must be re-started to ensure transaction atomicity

B) Schedule S is non-recoverable and cannot ensure transaction atomicity

C) Only T2 must be aborted and then re-started to ensure transaction atomicity

D) Schedule S is recoverable and can ensure atomicity and nothing else needs to be done

Databases · Transactions and Concurrency Control

Official IIT answer key · IIT Kanpur · Audited Aug 2026

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GATE CSE 2015 Set 3 Q29 · MCQ · 2 marks

Consider the following partial Schedule $S$ involving two transactions $T1$ and $T2$ . Only the read and the write operations have been shown. The read operation on data item $P$ is denoted by $read(P)$ and the write operation on data item $P$ is denoted by $write(P)$ . Suppose that the transaction $T1$ fails immediately after time instance 9. Which one of the following statements is correct?

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Key concept

Transactions and Concurrency Control

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How GATE tests Transactions and Concurrency Control

Across 2012–2026, Transactions and Concurrency Control in GATE CS is heavily weighted towards testing precedence (serialization) graphs for conflict serializability, schedule classification (recoverable, cascadeless, strict), and locking/timestamping protocol mechanics. Questions frequently present interleaved schedules and require students to identify conflict edges, count valid topological orders, or detect recovery anomalies such as dirty reads and cascading rollbacks. Recent exams (2021–2025) feature multiple MSQs testing theoretical invariants of Two-Phase Locking (2PL), deadlock prevention protocols (Wait-Die, Wound-Wait), and real-world ACID violations.

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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.

Databases · Transactions and Concurrency Control

Official IIT answer key · IIT Kanpur · Audited Aug 2026

Take topic test

GATE CSE 2015 Set 3 Q29 · MCQ · 2 marks

Consider the following partial Schedule $S$ involving two transactions $T1$ and $T2$ . Only the read and the write operations have been shown. The read operation on data item $P$ is denoted by $read(P)$ and the write operation on data item $P$ is denoted by $write(P)$ . Suppose that the transaction $T1$ fails immediately after time instance 9. Which one of the following statements is correct?

Select an option to check

Key concept

Transactions and Concurrency Control

Step-by-step verified solution

Examiner trap & misconception

Topic notes

How GATE tests Transactions and Concurrency Control

Full Transactions and Concurrency Control guide →

More on Transactions and Concurrency Control

All 25 questions on Transactions and Concurrency Control →

Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.

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