Consider the following schedule: S: r1(A), r2(B), X, w1(C), w2(A)

Question

How many operations (Read/ Write) can be placed in ‘X’ to make ‘S’, not conflict serializable?

Answer 1

one read (R2C), two write(W2C) ,      W1(B)  will make the schedule not CS

HOW

IF U DRAW DEPENDENCY GRAPH AS PER OUR SCHEDULE THEN THERE IS AN ARROW FROM

 T1 TO T2.

NOW IF WE PUT SOME VALUE IN PLACE OF X SUCH THAT THERE WILL BE AN ARROW FROM

T2 TO T1.

THEN THERE IS A CYCLE.WHICH LEADS TO NOT CS

NOW THINK:

IN T1 THERE IS W1(C). THEN WHAT VALUE IN PLACE OF X WILL MAKE A DEPENDENCY FROM T2 TO T1

THAT WILLL BE R2(C)   OR    W2(C)

AND 

IN T2 THERE IS R2(B).THEN WHAT VALUE IN PLACE OF X WILL MAKE A DEPENDENCY FROM T2 TO T1

THAT WILL BE W1(B)

IF U R CONFUSING WITH THE DESCRIPTION THE DRAW THE TRANSACTION...

Comments

3

W1(B)

R2(C)

W2(C)

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THANKS ..CORRECTED NOW