GATE CSE 2003 | Question: 87

Question

Consider three data items $D1, D2,$ and $D3,$ and the following execution schedule of transactions $T1, T2,$ and $T3.$ In the diagram, $R(D)$ and $W(D)$ denote the actions reading and writing the data item $D$ respectively.
$$ \begin{array}{|l|l|l|}\hline \textbf{T1}  &  \textbf{T2} & \textbf{T3}  \\\hline \text{} & \text{R(D3);} & \text{}\\ \text{} & \text{R(D2);} & \text{} \\ \text{} & \text{W(D2);} & \text{} \\ \text{} & \text{} & \text{R(D2);} \\ \text{} & \text{} & \text{R(D3);} \\ \text{R(D1);} & \text{} & \text{} \\ \text{W(D1);} & \text{} & \text{} \\ \text{} & \text{} & \text{W(D2);} \\ \text{} & \text{} & \text{W(D3);} \\ \text{} & \text{R(D1);} & \text{} \\ \text{R(D2);} & \text{} & \text{}   \\ \text{W(D2);} & \text{} & \text{} \\ \text{} & \text{W(D1);} & \text{}\\\hline \end{array}$$Which of the following statements is correct?

• A. The schedule is serializable as $T2; T3; T1$

• B. The schedule is serializable as $T2; T1; T3$

• C. The schedule is serializable as $T3; T2; T1$

• D. The schedule is not serializable

Comments

@Abhrajyoti00 can u explain the polygraph for this ? and there are some schedules that are not vs and not cs but still serializable so what about them how can we check them ?

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Serializable check is very easy. Just see if you can serialize the schedule. It means if T1-T2 or T2-T1 any one of the serial schedule can be made such that there's no change in database as the original one, then it is serializable. You can see @Deepak Poonia Sir's explanation on Serializability in Go classes YT channel.

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@Abhrajyoti00 can u plz send the link here as i am not able to see it on yt channel ?

Answer 1

It is true that It is NOT CSS

Now we know

(!CSS) and (!BW) ==> (!VSS)

This Schedule is not css as well as there is no BW therefore it is also not a VSS

Therefore It is Not a serializble Schedule.

Answer 2

APPROPIATE OPTION IS D IS  CORRECT