Suppose a database system crashes again while recovering from a previous crash. Assume checkpointing is not done by the database either during the transactions or during recovery.

Which of the following statements is/are correct?

Let r_{i}(z) and w_{i}(z) denote read and write operations respectively on a data item z by a transaction T_{i}. Consider the following two schedules.

S_{1} : r_{1}(x) r_{1}(y) r_{2}(x) r_{2}(y) w_{2}(y) w_{1}(x)

S_{2} : r1(x) r_{2}(x) r2(y) w2(y) r_{1}(y) w1(x)

Which one of the following options is correct?

_{1}and T

_{2}:

Here, RX stands for “Read(X)” and WX stands for “Write(X)”. Which one of the following schedules is conflict equivalent to the above schedule?

_{1}and T

_{2}

` S = r`_{2}(X); r_{1}(X); r_{2}(Y); w_{1}(X); r_{1}(Y); w_{2}(X); a_{1}; a_{2}

where r_{i}(Z) denotes a read operation by transaction T_{i} on a variable Z, w_{i}(Z) denotes a write operation by T_{i} on a variable Z and a_{i} denotes an abort by transaction T_{i}
.

Which one of the following statements about the above schedule is **TRUE**?