Test by Bikram | Mock GATE | Test 2 | Question: 51

Question

Which of the following schedules are conflicts serializable?

1. S1:   $r1$ $\left ( A \right )$, $r1$$\left ( B \right )$, $w2$$\left ( A \right )$, $r3$ $\left ( A \right )$, $w1$$\left ( B \right )$, $w3$ $\left ( A \right )$, $r2$ $\left ( B \right )$, $w2$$\left ( B \right )$
2. S2 :  $r1$$\left ( A \right )$, $r2$$\left ( A \right )$, $r3$ $\left (B \right )$, $w1$$\left ( A \right )$, $r2$ $\left ( C \right )$, $r2$ $\left (B \right )$, $w2$ $\left (B \right )$, $w1$$\left ( C \right )$
3. S3:   $w3$$\left ( A \right )$ , $r1$ $\left ( A \right )$, $w1$ $\left (B \right )$, $r2$$\left (B \right )$, $w2$ $\left ( C \right )$, $r3$, $\left ( C \right )$

• A. $S1,S3$ only
• B. $S2,S3$ only
• C. $S1,S2$ only
• D. $S1, S2, S3$

Answer 1

S1: Precedence graph , No cycle: So conflict serializable.
S2:  Precedence graph ,  No cycle: Conflict serializable.
S3: Precedence graph , Cycle: Not conflict serializable

Comments

Think C does not have a cycle

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S3 does have a cycle so it is not conflict serializable , option C is correct.

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where is the cycle in s3

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cycle in 3rd transaction is as follow

 w3(A) -> r1(A)    w1(B) -> r2(B)  w2(C) -> r3(C)

   3      ->   1         1     ->  2         2    ->   3