Consider the following four schedules due to three transactions (indicated by the subscript) using read and write on a data item X, denoted by r(X) and w(X) respectively. Which one of them is conflict serializable ?

S1: r1(X); r2(X); w1(X); r3(X); w2(X)

S2: r2(X); r1(X); w2(X); r3(X); w1(X)

S3: r3(X); r2(X); r1(X); w2(X); w1(X)

S4: r2(X); w2(X); r3(X); r1(X); w1(X)

(A) S₁
(B) S₂
(C) S₃
(D) S₄


Answer: (D)

Explanation: We can draw precedence graph for each schedule and for conflict serializability graph must not contain cycle.

Refer:Gate_CS 2014
So, option (D) is correct.


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