Exams › GATE › Technical
A schedule of three database transactions T1, T2, and T3 is shown. Ri(A) and Wi(A) denote read and write of data item A by transaction Ti, i = 1,2,3. The transaction T1 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)
- Only T2
- Only T3
- Both T2 and T3
- Neither T2 nor T3
Correct answer: Both T2 and T3
Solution
T1 writes Y then aborts. T2 reads Y (R2(Y)) after W1(Y), a dirty read, so T2 must roll back. T3 also reads Y (R3(Y)) which carries T1's uncommitted value, so T3 must roll back too. Both T2 and T3 are rolled back.
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