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Consider the following schedules involving two transactions. Which one of the following statements is TRUE?

  • $S_1 :r_1(X); r_1(Y); r_2(X); r_2(Y); w_2(Y); w_1(X)$
  • $S_2 :r_1(X); r_2(X); r_2(Y); w_2(Y); r_1(Y); w_1(X)$
  1. Both $S_1$ and $S_2$ are conflict serializable.

  2. $S_1$ is conflict serializable and $S_2$ is not conflict serializable.

  3. $S_1$ is not conflict serializable and $S_2$ is conflict serializable.

  4. Both $S_1$ and $S_2$ are not conflict serializable.

asked in Databases by Veteran (59.5k points) | 1.4k views

5 Answers

+21 votes
Best answer

For $S1$ : it is not conflict serializable 

for $S2$ : it is conflict serializable

Answer is option C.

answered by Boss (30.7k points)
edited by
+7 votes
You can make a Precedence graph for the two schedules.And check for the conflicts pairs making a Cycle.

S1 makes a cycle. T1-->T2 and T2-->T1. And hence is not Conflict Serializable.

S2 does not makes cycle and has transition from T2-->T1 only. And hence is Conflict Serializable.

Conflict Pairs: RW, WR, WW.
answered by Boss (19.7k points)
+3 votes
Ans - Option C

In S1: RW conflict from 1-2 and 2-1 so It is not C.S.

In S2: RW conflict AND WR conflict from 2-1 only so it is C.S.
answered by (429 points)
–5 votes
OPTION IS A
answered by Junior (609 points)
–5 votes
OPTION IS B IS APPROPIATE ONE
answered by Junior (609 points)
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