Transactions

Consider concurrent execution of two transactions $T 1$ and $T 2$ in a DBMS, both of which access a data object $A$. For these two transactions to not conflict on $A$, which one of the following statements must be true?

A schedule of three database transactions $T_1, T_2$, and $T_3$ is shown. $R_i(A)$ and $W_i(A)$ denote read and write of data item $A$ by transaction $T_i, i=1,2,3$. The transaction $T_1$ aborts at the end. Which other t...

An audit of a banking transactions system has found that on an earlier occasion, two joint holders of account $A$ attempted simultaneous transfers of Rs. 10000 each from account $A$ to account $B$. Both transactions read...

Once the DBMS informs the user that a transaction has been successfully completed, its effect should persist even if the system crashes before all its changes are reflected on disk. This property is called

Consider the following read-write schedule $S$ over three transactions $T_{1}$, $T_{2}$, and $T_{3}$, where the subscripts in the schedule indicate transaction IDs: $S: r_{1}(z); w_{1}(z); r_{2}(x); r_{3}(y); w_{3}(y); r...

Which of the following statements about the Two Phase Locking (2PL) protocol is/are TRUE?

Let R i (z) and W i (z) denote read and write operations on a data element z by a transaction T i , respectively. Consider the schedule S with four transactions. S : R 4 (x), R 2 (x), R 3 (x), R 1 (y), W 1 (y), W 2 (x),...

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 : r 1 (x) r 2...

Let S be the following schedule of operations of three transactions T 1 , T 2 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 statemen...

Consider the following two statements about database transaction schedules: I. Strict two-phase locking protocol generates conflict serializable schedules that are also recoverable. II. Timestamp-ordering concurrency con...

Suppose a database schedule $$S$$ involves transactions $${T_1},\,...,\,{T_n}.$$ Construct the precedence graph of $$S$$ with vertices representing the transactions and edges representing the conflicts. If $$S$$ is seria...

Consider the following database schedule with two transactions, T 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...

Consider the following two phase locking protocol. Suppose a transaction $$T$$ accesses (for read or write operations), a certain set of objects $$\left\{ {{O_1},...,{O_k}} \right\}.$$ This is done in the following manne...

Which one of the following is NOT a part of the $$ACID$$ properties of database transactions?

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 th...

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?

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);...

Consider the following transactions with data items P and Q initialized to zero: T 1 : read (P) ; read (Q) ; if P = 0 then Q : = Q + 1 ; write (Q). T 2 : read (Q) ; read (P) if Q = 0 then P : = P + 1 ; write (P). Any non...

Which of the following concurrency control protocols ensure both conflict serializability and freedom from deadlock? I. 2-phase locking II. Time-stamp ordering

Consider two transactions T 1 and T 2 and four schedules S 1 , S 2 , S 3 , S 4 of T 1 and T 2 as given below: T 1 : R 1 [ x ] W 1 [ x ] W 1 [ y ] T 2 : R 2 [ x ] R 2 [ y ] W 2 [ y ] S 1 : R 1 [ x ] R 2 [ x ] R 2 [ y ] W...

Consider the following three schedules of transactions T 1 , T 2 and T 3 . [ Notation: In the following NYO represents the action Y (R for read, W for write) performed by transac­tion N on object O. ] (S1) 2RA 2WA 3RC 2W...

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 (Y); r 2 (X); w 2 (Y); w 1 (X); S 2 : r 1 (X); r 2 (X); r 2 (Y); w 2 (Y); r 1 (Y); w...

Consider the following two transactions: T 1 and T 2 . T 1 : read (A); T 2 : read (B); read (B); read (A); if A = 0 then B ← B + 1; if B ≠ 0 then A ← A - 1; write (B); write (A); Which of the following schemes, using sha...

Amongst the ACID properties of a transaction, the 'Durability' property requires that the changes made to the database by a successful transaction persist

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 = (salespe...

Which level of locking provides the highest degree of concurrency in a relational database?

Which of the following scenarios may lead to an irrecoverable error in a database system?