Give examples of schedules that would be accepted at
a. SNAPSHOT isolation but not REPEATABLE READ.
b. SERIALIZABLE but not SNAPSHOT isolation. (Hint: T2 performs a write after T1 has committed.)
a. r1(x) r1(y) w1(x) r2(y) r2(x) w1(y) commit2 commit1
A deadlock would occur at REPEATABLE READ.
b. r1(x) r1(y) r2(y) w1(x) commit1 r2(x) w2(x) commit2
This schedule is serializable, but would not be allowed in SNAPSHOT isolation, because both concurrent transactions updated x.
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