Let ri(z) and wi(z) denote read and write operations respectively on a data item z by a transaction Ti. Consider the following two schedules. S1 : r1(x)\ r1(y)\ r2(x)\ r2(y)\ w2(y)\ w1(x) S2 : r1(x)\ r2(x)\ r2(y)\ w2(y)\ r1(y)\ w1(x) Which one of the following options is correct? A) S1 is conflict serializable, and S2 is not conflict serializable. B) S1 is not conflict serializable, and S2 is conflict serializable. C) Both S1 and S2 are conflict serializable. D) Neither S1 nor S2 is conflict serializable.

Official answer: B) S1 is not conflict serializable, and S2 is conflict serializable.. Explanation: To check for conflict serializability, we construct the precedence (serialization) graph for each schedule: 1. Schedule S1: - Conflicting operations on item y: r1(y) is executed before w2(y), which creates a directed edge T1 T2. - Conflicting operations on item x: r2(x) is executed before w1(x), which creates a directed edge T2 T1. - The precedence graph contains a cycle: T1 T2. Therefore, S1 is not conflict serializable. 2. Schedule S2: - Conflicting operations on item y: w2(y) is executed before r1(y), which creates a directed edge T2 T1. - Conflicting operations on item x: r2(x) is executed before w1(x), which creates a directed edge T2 T1. - The precedence graph contains no cycle (only the edge T2 T1). Therefore, S2 is conflict serializable. Hence, S1 is not conflict serializable, and S2 is conflict serializable, which corresponds to option B.

A) S1 is conflict serializable, and S2 is not conflict serializable.

B) S1 is not conflict serializable, and S2 is conflict serializable.

C) Both S1 and S2 are conflict serializable.

D) Neither S1 nor S2 is conflict serializable.

Databases · Transactions and Concurrency Control

Official IIT answer key · IIT Bombay · Audited Aug 2026

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GATE CSE 2021 Set 1 Q32 · MCQ · 2 marks

Let $r_i(z)$ and $w_i(z)$ denote read and write operations respectively on a data item $z$ by a transaction $T_i$ . Consider the following two schedules. $S_1 : r_1(x)\ r_1(y)\ r_2(x)\ r_2(y)\ w_2(y)\ w_1(x)$ $S_2 : r_1(x)\ r_2(x)\ r_2(y)\ w_2(y)\ r_1(y)\ w_1(x)$ Which one of the following options is correct?

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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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Databases · Transactions and Concurrency Control

Official IIT answer key · IIT Bombay · Audited Aug 2026

Take topic test

GATE CSE 2021 Set 1 Q32 · MCQ · 2 marks

Let $r_i(z)$ and $w_i(z)$ denote read and write operations respectively on a data item $z$ by a transaction $T_i$ . Consider the following two schedules. $S_1 : r_1(x)\ r_1(y)\ r_2(x)\ r_2(y)\ w_2(y)\ w_1(x)$ $S_2 : r_1(x)\ r_2(x)\ r_2(y)\ w_2(y)\ r_1(y)\ w_1(x)$ Which one of the following options is correct?

Select an option to check

Key concept

Transactions and Concurrency Control

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Examiner trap & misconception

Topic notes

How GATE tests Transactions and Concurrency Control

Full Transactions and Concurrency Control guide →

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

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