Database Management System
Q181.
Consider the following transactions with data items P and Q initialized to zero: T1 :read (P); read (Q); if P = 0 then Q := Q + 1 ; write (Q). T2 : read (Q); read (P); if Q = 0 then P := P + 1 ; write (P). Any non-serial interleaving of T1 and T2 for concurrent execution leads toQ182.
Consider the transactions T1, T2, and T3 and the schedules S1 and S2 given below. T1 : r1(x); r1(Z) ; w1(x); w1(Z) T2 : r2(x); r2(Z); w2(Z) T3 : r3(x); r3(x); w3(Y) S1: r1(x); r3(Y); r3(x); r2(Y); r2(Z); w3(Y); w2(Z); r1(Z); w1(x); w1(Z) S2: r1(x); r3(Y); r2(Y); r3(x); r1(Z); r2(Z); w3(Y); w1(x); w2(Z); w1(Z) Which one of the following statements about the schedules is TRUE?Q183.
Consider the following four schedules due to three transactions (indicted 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?Q184.
Consider the following transaction involving two bank accounts x and y. read(x); x:=x-50; write(x); read(y); y:=y+50; write(y) The constraint that the sum of the accounts x and y should remain constant is that ofQ185.
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. S1: r_1(x)r_1(y)r_2(x)r_2(y)w_2(y)w_1(x) S2: r_1(x)r_2(x)r_2(y)w_2(y)r_1(y)w_1(x) Which one of the following options is correct?Q186.
Consider the following databases chedule with two transactions, T1 and T2. 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 avariable Z, w_{i}(Z) denotes a write operation by T_{i} on avariable Z and a_{i} denotes an abort by transaction T_{i}. Which one of the following statements about the above schedule is TRUE?Q188.
Two transactions T_1 \; and \; T_2 are given as: T_{1}:r_{1} (X)w_{1}(X)r_{1}(Y)w_{1}(Y) T_{2}:r_{2}(Y)w_{2}(Y)r_{2}(Z)w_{2}(Z) where r_{i}(V) denotes a read operation by transaction T_{i} on a variable V and w_{i}(V) denotes a write operations by transaction T_{i} on a variable V. The total number of conflict serializable schedules that can be formed by T_1 \; and \; T_2 is _____________.Q189.
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?Q190.
Let S be the following schedule of operations of three transactions T_1, T_2 \text{ and }T_3 in a relational database system: R_2(Y), R_1(X), R_3(Z), R_1(Y)W_1(X), R_2(Z), W_2(Y), R_3(X), W_3(Z) Consider the statements P and Q below: P: S is conflict-serializable. Q: If T_3 commits before T_1 finishes, then S is recoverable. Which one of the following choices is correct?