Transactions
Q31.
Which of the following contains complete record of all activity that affected the contents of a database during a certain period of time?Q32.
Consider the following three schedules of transactions T1, T2 and T3. [Notation: In the following NYO represents the action Y (R for read, W for write) performed by transaction N on object O.]\begin{array}{lllllllllll} \hline(S 1) & 2 R A & 2 W A & 3 R C & 2 W B & 3 W A & 3 W C & 1 R A & 1 R B & 1 W A & 1 W B \\ \hline(S 2) & 3 R C & 2 R A & 2 W A & 2 W B & 3 W A & 1 R A & 1 R B & 1 W A & 1 W B & 3 W C \\ \hline(S 3) & 2 R A & 3 R C & 3 W A & 2 W A & 2 W B & 3 W C & 1 R A & 1 R B & 1 W A & 1 W B \\ \hline \end{array}Which of the following statements is TRUE?Q34.
Amongst the ACID properties of a transaction, the 'Durability' property requires that the changes made to the database by a successful transaction persistQ35.
Consider the following log sequence of two transactions on a bank account, with initial balance 12000,that transfer 2000 to a mortgage payment and, then apply a 5% interest. 1. T1 start 2. T1 B old = 12000 new = 10000 3. T1 M old = 0 ne = 2000 4. T1 commit 5. T2 start 6. T2 B old = 10000 new = 10500 7. T2 commit Suppose the database system crashed just before log record 7 is written. When the system is restarted, which one statement is true of the recovery procedure?Q36.
A company maintains records of sales made by its salespersons and pays them commission based on each individual's total sales made in a year. This data is maintained in a table with following schema: salesinfo = (salespersonid, totalsales, commission) In a certain year, due to better business results, the company decides to further reward its salespersons by enhancing the commission paid to them as per the following formula: If commission \leq 50000, enhance it by 2% If 50000 < commission [latex]\leq 100000[/latex], enhance it by 4% If commission > 100000, enhance it by 6% The IT staff has written three different SQL scripts to calculate enhancement for each slab, each of these scripts is to run as a separate transaction as follows: T1 Update salesinfo Set commission = commission * 1.02 Where commission < = 50000; T2 Update salesinfo Set commission = commission * 1.04 Where commission > 50000 and commission is < = 100000; T3 Update salesinfo Set commission = commission * 1.06 Where commission > 100000; Which of the following options of running these transactions will update the commission of all salespersons correctlyQ37.
Consider the following schedules involving two transactions. Which one of the following statements is TRUE? S_1 :r_1(X); r_1(Y); r_2(X); r_2(Y); w_2(Y); w_1(X) S_2 :r_1(X); r_2(X); r_2(Y); w_2(Y); r_1(Y); w_1(X)Q38.
Consider the following two transactions : T1 and T2. T1:read (A); read (B); if A = 0 then B \leftarrow B + 1; write (B); T2 : read (B); read (A); if B \neq 0 then A \leftarrow A - 1; write (A); Which of the following schemes, using shared and exclusive locks, satisfy the requirements for strict two phase locking for the above transactions?Q39.
Consider the following schedule S of transactions T1 and T2:{\begin{array}{l|l} \textbf{T1}& \textbf{T2} \\\hline \text{Read(A)} \\ \text{A = A ? 10}\\ & \text{Read(A) }\\ & \text{Temp = 0.2*A} \\ & \text{Write(A)} \\ & \text{Read(B)} \\ \text{Write(A)}\\ \text{Read(B)}\\ \text{B = B + 10}\\ \text{Write(B)} \\ & \text{B = B + Temp} \\ & \text{Write(B)}\\ \end{array}}Which of the following is TRUE about the schedule S ?Q40.
Which of the following scenarios may lead to an irrecoverable error in a database system?