253 views
0 votes
0 votes
My doubt is ... when checking serializbility why do we check conflict and view serializability ..i mean result equivalence would be better ... no doubt it would be more complex but if any transaction is giving the same result as serial schedule then its ok ... secondly can there be a schedule  which has different order of conflicting operations but same result ?? in that case would it be equivalent to serial schedule ??

1 Answer

Best answer
1 votes
1 votes

1] Why not use result equivalence?

$\rightarrow$ Serial schedules need not be result equivalent.

Consider this simple example with 2 transaction T1 and Twhere x = 100 initially;

S1 : T1(x=x+100);T2(x=x/2) Result: x=100

S2 : T2(x=x/2);T1(x=x+100) Result: x=150

$\rightarrow$ Now if we go with result equivalence then we have to compare result of concurrent schedule with every possible serial schedule. This is hell of a computation.

Also, there is redundency in calculation. I mean, consider the fact that data item (x here) will have dynamic value. As value of x is not fixed, we will have to calculate result of every serial schedule everytime and compare it with concurrent schedule. Now, as we are computing every serial schedule why do it concurrently again??!

2] Can there be a schedule which has different order of conflicting operations but same result ?

$\rightarrow$ Yes, there is a possibility of this. (You think of the example ;-) )

It would be called as result equivalent but not conflict equivalent.

selected by

Related questions

0 votes
0 votes
0 answers
1
SakarKoot asked Sep 4, 2022
228 views
What is Proof/Explanation for complexity to test if a schedule is conflict serializable is O(n^2) whereas for view serializable is O(2^n)-Exponential ?
0 votes
0 votes
1 answer
2
atulcse asked Jan 10, 2022
381 views
Consider the following schedule:R2(A), R1(A), R3(B), W3(B), W2(A), R1(A)Is the above schedule view serializable?
0 votes
0 votes
1 answer
3
atulcse asked Nov 2, 2021
433 views
Can a schedule be serializable if it is not view serializable? Are conflict equivalence and view equivalence the only two ways to decide if a schedule is serializable?
1 votes
1 votes
1 answer
4
Na462 asked Jan 13, 2019
1,472 views
Consider following Schedule S with data item x :S : W1(X) R2(X) W3(X) R4(X) W5(X) R6(X) W7(X) R8(X) W9(X) R10(X)The number of schedule view equivalent to Schedule S but n...