Consider the schedule S: t1: R2(X), R3(Y); t2: W2(X), W3(Y); t3: R1(Y), R4(X); t4: W1(Y), W4(X); t5: R3(X); t6: W3(X). Choose the correct serial execution order equivalent to S.
Pick an option to check yourself, or open the answer below.
Show answer & explanation
Correct answer: C. T2-T4-T3-T1
Explanation
On X: T2 (t1–t2) → T4 (t3–t4) → T3 (t5–t6). On Y: T3 (t1–t2) → T1 (t3–t4). The precedence graph has edges T2 → T4 → T3 → T1, so the equivalent serial order is T2, T4, T3, T1.
Note on the official key: the official key says option B. Official/PW key is B (T2-T3-T1-T4), but in that order T3 would read X before T4 writes it, whereas in S T3 reads T4's value.
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