Consider the following schedules,

S1: R1(A)W2(B)R2(A)W1(B)W3(B)W1(C)R3(B)W1(A) 
S2: W2(C)R1(A)W3(B)R1(C)R3(B)R3(A)W1(B)
S3: R3(B)R2(A)R1(A)R2(C)W3(A)W2(B)W1(C)
S4: W1(A)W2(B)W1(B)W2(A) 

Which of the following schedule are conflict serializable?
(A) Only S1 and S3
(B) Only S1 and S2
(C) Only S2 and S4
(D) Only S2 and S3


Answer: (B)

Explanation: Using Precedence graphs for given schedules,

S1: R1(A)W2(B)R2(A)W1(B)W3(B)W1(C)R3(B)W1(A) 

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Serializable as T2 → T1 → T3.

S2: W2(C)R1(A)W3(B)R1(C)R3(B)R3(A)W1(B) 

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Serializable as either T2 → T3 → T1 or T3 → T2 → T1.

S3: R3(B)R2(A)R1(A)R2(C)W3(A)W2(B)W1(C) 

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Cycle exist, so can not be conflict serializable.

S4: W1(A)W2(B)W1(B)W2(A) 

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Cycle exist, so can not be conflict serializable.

Therefore, option (B) is correct.

Quiz of this Question


  • Last Updated : 30 Nov, 2018

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