1
GATE CSE 2009
+2
-0.6
Consider two transactions T1 and T2 and four schedules S1, S2, S3, S4 of T1 and T2 as 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 above schedules are conflict-serializable?
A
S1 and S2
B
S2 and S3
C
S3 only
D
S4 only
2
GATE CSE 2009
+2
-0.6
Let R and S be relational schemes such that R = { a, b, c } and S = { c }. Now consider the following queries on the database:

I. $$\pi_{R-S}(r) - \pi_{R-S} \left (\pi_{R-S} (r) \times s - \pi_{R-S,S}(r)\right )$$

II. $$\left\{t \mid t \in \pi_{R-S} (r) \wedge \forall u \in s \left(\exists v \in r \left(u = v[S] \wedge t = v\left[R-S\right]\right )\right )\right\}$$

III.$$\left\{t \mid t \in \pi_{R-S} (r) \wedge \forall v \in r \left(\exists u \in s \left(u = v[S] \wedge t = v\left[R-S\right]\right )\right ) \right\}$$

IV. Select R.a, R.b
From R, S
Where R.c = S.c
Which of the above queries are equivalent?
A
I and II
B
I and III
C
II and IV
D
III and IV
3
GATE CSE 2008
+2
-0.6
Consider the following three schedules of transactions T1, T2 and T3.
[ Notation: In the following NYO represents the action Y (R for read, W for write) performed by transac­tion N on object O. ]

(S1) 2RA 2WA 3RC 2WB 3WA 3WC 1RA 1RB 1WA 1WB

(S2) 3RC 2RA 2WA 2WB 3WA 1RA 1RB 1WA 1WB 3WC

(S3) 2RZ 3RC 3WA 2WA 2WB 3WC 1RA 1RB 1WA 1WB

Which of the following statements is TRUE?
A
S1, S2 and S3 are all conflict equivalent to each other
B
No two of S1, S2 and S3 are conflict equivalent to each other
C
S2 is conflict equivalent to S3, but not to S1
D
S1 is conflict equivalent to S2, but not to S3
4
GATE CSE 2007
+2
-0.6
Consider the following schedules involving two transactions. Which one of the following statements is TRUE?

S1: r1(X); r1(Y); r2(Y); r2(X); w2(Y); w1(X);

S2: r1(X); r2(X); r2(Y); w2(Y); r1(Y); w1(X);

A
Both S1 and S2 are conflict serializable.
B
S1 is conflict serializable and S2 is not conflict serializable.
C
S1 is not conflict serializable and S2 is conflict serializable.
D
Both S1 and S2 are not conflict serializable.
GATE CSE Subjects
EXAM MAP
Medical
NEET