The topic is concurrency control:

A. What happens for the following events if a multiversion, timestamp scheduler is used? What happens if the scheduler does not maintain multiple versions?

1) st1, st2, r1(A), r2(B), w2(A), w1(B).

2) st1, st2, st3, r1(A), r2(B), w1(C), r3(B), r3(C), w2(B), w3(A).

3) st1, st2, st3, r1(A), r3(B), w1(C), r2(B), r2(C), w3(B), w2(A).

where wi(X) means that transaction i writes item X, and ri(X) means that transaction i reads item X, sti means that transaction i starts.

B. What happens for the following events if a validation-based scheduler is used?

1) R1(A,B), R2(B,C), V1, R3(C,D), V3, W1(A), V2, W2(A), W3(B).

2) R1(A,B), R2(B,C), V1, R3(C,D), V3, W1(C), V2, W2(A), W3(D).

3) R1(A,B), R2(B,C), R3(C), V1, V2, V3, W1(A), W2(C), W3(B).

where Ri(X) means that transaction i starts and its read set is X, Vi means that Ti attempts to validate, and Wi(X) means that Ti finishes and its write set was X.

C. What are all the ways to insert locks (of a single type only) into the sequence of actions r1(A), r1(B), w1(A), w1(B) so that the transaction is

Strict two-phase locked

Two-phase locked (not strict).

where the notation is as in A.

D. Assume shared locks are requested immediately before each read, and exclusive locks immediately before each write. Unlocks occur immediately after the final action of the respective transaction. Which actions are denied?

r1(A), r2(B), w1(C), r3(D), r4(E), w3(B), w2(C), w4(A), w1(D)

r1(A), r2(B), w1(C), w2(D), r3(C), w1(B), w4(D), w2(A)

where the notation is as in A.

Please provide explanations as well. Many thanks in advance.