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GATE CSE 2025 Session 1 Q15: Cascading rollback after T1 aborts

Question

A schedule of three database transactions T1T_1, T2T_2, and T3T_3 is shown. Ri(A)R_i(A) and Wi(A)W_i(A) denote read and write of data item AA by transaction TiT_i, i=1,2,3i = 1, 2, 3. The transaction T1T_1 aborts at the end. Which other transaction(s) will be required to be rolled back?

R1(X)W1(Y)R2(X)R2(Y)R3(Y)ABORT(T1)R_1(X) \quad W_1(Y) \quad R_2(X) \quad R_2(Y) \quad R_3(Y) \quad \text{ABORT}(T_1)

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Answer: C (official GATE 2025 final answer key)

Concept used: Cascading rollback: any transaction that read a value written by an aborted transaction must also be rolled back.

First step: Find who read data written by T1T_1: T1T_1 wrote YY, and both R2(Y)R_2(Y) and R3(Y)R_3(Y) come after it.

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Source: official GATE 2025 Session 1 CS question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key

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