Transactions
Q21.
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?Q23.
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 _____________.Q24.
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?Q25.
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?Q26.
Which of the following concurrency control protocols ensure both conflict serializability and freedom from deadlock? I. 2-phase locking II. Time-stamp orderingQ28.
Consider a schedule of transactions T1 and T2: 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?Q29.
Which of the following scenarios may lead to an irrecoverable error in a database system?Q30.
Consider two transactions T1 and T2, and four schedules S1, S2, S3, S4 of T1 and T2 as given below: T_{1}:R_{1}[x]W_{1}[x]W_{1}[y] T_{2}:R_{2}[x]R_{2}[x]W_{1}[y] S_{1}:R_{1}[x]R_{2}[x]R_{2}[y]W_{1}[x]W_{1}[y]W_{2}[y] S_{2}:R_{1}[x]R_{2}[x]R_{2}[y]W_{1}[x]W_{2}[y]W_{1}[y] S_{3}:R_{1}[x]W_{1}[x]R_{2}[x]W_{1}[y]R_{2}[y]W_{2}[y] S_{4}:R_{2}[x]R_{2}[y]R_{1}[x]W_{1}[x]W_{1}[y]W_{2}[y] Which of the above schedules are conflict-serializable?