Databases System. The complete book. Exercise 18.4.1 For parts (a) and (c). of the schedules of transactions T₁, T₂, and T3 below:

a) r₁ (A); r2 (B); r₃(C); w1(B); w2 (C); w₃(D);

c) r₁(A); r₂(B); r3 (C); r₁(B); r₂(C); r3 (D); w1 (C); w2 (D); w3 (E);

Question. Do each of the following:

i. Insert shared and exclusive locks, and insert unlock actions. Place a shared lock immediately in front of each read action that is not followed by a write action of the same element by the same transaction. Place an exclusive lock in front of every other read or write action. Place the necessary unlocks at the end of every transaction.

ii. Tell what happens when each schedule is run by a scheduler that supports shared and exclusive locks.

iii. Insert shared and exclusive locks in a way that allows upgrading. Place a shared lock in front of every read, an exclusive lock in front of every write, and place the necessary unlocks at the ends of the transactions.

iv. Tell what happens when each schedule from (iii) is run by a scheduler that supports shared locks, exclusive locks, and upgrading.

v. Insert shared, exclusive, and update locks, along with unlock actions. Place a shared lock in front of every read action that is not going to be upgraded, place an update lock in front of every read action that will be

upgraded, and place an exclusive lock in front of every write action. Place unlocks at the ends of transactions, as usual.

vi. Tell what happens when each schedule from (v) is run by a scheduler that supports shared, exclusive, and update locks.