#dbms #transaction

Question

Consider the 2 transactions T1 and T2 and four schedules S1, S2, S3 and S4 of T1 and T2 are
given below:
T1: R1[X] W1[X] W1[Y]
T2: R2[X] R2[Y] W2[Y]
S1: R1[X] R2[X] R2[Y] W1[X] W1[Y] W2[Y]
S2: R1[X] R2[X] R2[Y] W1[X] W2[Y] W1[Y]
S3: R1[X] W1[X] R2[X] W1[Y] R2[Y] W2[Y]
S4: R2[X] R2[Y] R1[X] W1[X] W1[Y] W2[Y]
Which of the following schedules are conflict serializable?
(a) S1 and S2 (b) S2 and S3
(c) S3 only (d) S4 only

Comments

only S2 and S3 are conflict serializable.

Answer 1

b)  option answer 

Answer 2

(B)
There can be two possible serial schedules T1 T2 and T2 T1. The serial schedule T1 T2 has the following sequence of operations
R1[X] W1[X] W1[Y] R2[X] R2[Y] W2[Y]
And the schedule T2 T1 has the following sequence of operations.
R2[X] R2[Y] W2[Y] R1[X] W1[X] W1[Y]
The Schedule S2 is conflict-equivalent to T2 T1 and S3 is conflict-equivalent to T1 T2.