1.Why is an explicit transaction end statement needed in SQL but not an explicit
begin statement? 2. Describe situations where each of the different isolation levels would be useful for transaction processing. 3. Which of the following schedules is (conflict) serializable? For each serializable schedule, determine the equivalent serial schedules.
a. rl(X); r3(X); WI(X); r2(X); W3(X);
b. r l (X); r3(X); W3(X); WI(X); r2(X);
c. r3(X); r2(X); W3(X); r l (X); WI(X);
d. r3(X); r2(X); rl (X); W3(X); WI(X);
4. Consider the three transactions T I, T2, and T3, and the schedules 51 and 52 given
below. Draw the serializability (precedence) graphs for 51 and 52′ and state
whether each schedule is serializable or not. If a schedule is serializable, write
down the equivalent serial schedule(s).
T I: rl (X); r l (2); WI (X);
T2: r2 (2); r2 (Y); W2 (2); W2 (Y);
T3: r3 (X); r3 (Y); W3 (Y);
51: rl (X); r2 (2); rl (2); r3 (X); r3 (Y); WI (X); W3 (Y); r2 (Y); W2 (2); W2 (Y);
52: rl (X); r2 (2); r3 (X); rl (2); r2 (Y); r3 (Y); WI (X); W2 (2); W3 (Y); W2 (Y);