GATE | GATE CS 2021 | Set 1 | Question 42

Let ri(z) and wi(z) denote read and write operations respectively on a data item z by a transaction Ti. Consider the following two schedules.

S1:  r1(x)r1(y)r2(x)r2(y)w2(y)w1(x)
S2:  r1(x)r2(x)r2(y)w2(y)r1(y)w1(x) 

Which one of the following options is correct?
(A) S1 is conflict serializable, and S2 is not conflict serializable
(B) S1 is not conflict serializable, and S2 is conflict serializable
(C) Both S1 and S2 are conflict serializable
(D) Neither S1 nor S2 is conflict serializable

Answer: (B)
Explanation:

S1
T1	T2
r(x)
r(y)
	r(x)
	r(y)
	w(y)
w(x)

S2
T1	T2
r(x)
	r(x)
	r(y)
	w(y)
r(y)
w(x)

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