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)
1
S1
2
S2
3
S3
4
S4