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GATE CSE 2025 Session 2 Q53: Which interleavings of T1 and T2 are conflict serializable

Question

Consider the database transactions T1 and T2, and data items X and Y. Which of the schedule(s) is/are conflict serializable?

Transaction T1Transaction T2
R1(X)W2(X)
W1(Y)W2(Y)
R1(X)COMMIT(T2)
W1(X)
COMMIT(T1)

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Answer: B (official GATE 2025 final answer key)

Concept used: A schedule is conflict serializable when its precedence graph has no cycle.

First step: For each schedule, add an edge for every pair of conflicting operations (same item, at least one write) in their order, and look for edges both ways between T1 and T2.

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Source: official GATE 2025 Session 2 CS question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key

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