Test by Bikram | Databases | Test 2 | Question: 19

Question

A schedule with two transactions T1 and T2 is as mentioned below:

$\begin{array}{|c|c|} \hline T1 & T2 \\ \hline \text{read(A)} & {} \\  \hline \text{write(A)} & {} \\ \hline {} & \text{read(A)} \\ \hline {} & \text{commit} \\ \hline \text{read(A)} & {} \\ \hline \text{abort} & {} \\ \hline \end{array}$

The above schedule is an example of:

• A. Cascade-less schedule
• B. Recoverable schedule
• C. Both Cascade-less and Recoverable schedule
• D. Irrecoverable schedule

Comments

Irrecoverable; since a dirty read has been performed.

Not cascadeless, because a transaction read an item from an uncommitted transaction.

 

 

Answer 1

T2 reads a value which is written by T1, and commits before T1. So, if T1 faces any error and aborts after T2 commits (as in the last line of schedule), T1 will be rolled back, but T2 is not able to roll back since it is already committed.

So, we have an irrecoverable schedule.