Consider the schedule S (operations at successive timestamps t1–t6):
t1: T2 R(X), T3 R(Y)
t2: T2 W(X), T3 W(Y)
t3: T1 R(Y), T4 R(X)
t4: T1 W(Y), T4 W(X)
t5: T3 R(X)
t6: T3 W(X)
Choose the correct (conflict-equivalent) serial execution order for the schedule S.
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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 T2 → T4 → T3 → T1 (plus T2 → T3) is acyclic, and its topological order is T2, T4, T3, T1. (Some published keys print T2-T3-T1-T4, but that order would put T3 before T4, contradicting T4 W(X) preceding T3 R(X).)More Database Management Systems questions
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