GATE CS 2017 Set 2 Q44 — Transactions and Concurrency Control

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 transaction(s) will be required to be rolled back? …

Consider the database transactions T1 and T2 , and data items X and Y . Which of the schedule(s) is/are conflict serializable? …

​​​​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 the same value, Rs.$11000$, as the initial balance in $A$ and were allowed to go through. $B$ was credited Rs.$10000$ …

​​​​Consider the following read-write schedule $\text{S}$ over three transactions $T_{1}, T_{2}$, and $T_{3}$, where the subscripts in the schedule indicate transaction IDs: $S: r_{1}(z) ; w_{1}(z) ; r_{2}(x) ; r_{3}(y) ; w_{3}(y) ; r_{2}(y) ; w_{2}(x) ; w_{2}(y) ;$ Which of the following transaction schedules is/are conflict equivalent to …

​​​​​Once the $\text{DBMS}$ 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