![GATE CSE 2020 Database Management System - Transactions and Concurrency Question 7 English](https://imagex.cdn.examgoal.net/1da9i2ynkcu2d4qa/400c524c-3a46-4b39-babf-4f7b2b8996b6/2fc71120-ca49-11ea-b796-4745b429ed6f/file-1da9i2ynkcu2d4qb-500w.png)
Here, RX stands for “Read(X)” and WX stands for “Write(X)”. Which one of the following schedules is conflict equivalent to the above schedule?
S = r2(X); r1(X); r2(Y); w1(X); r1(Y); w2(X); a1; a2
where ri(Z) denotes a read operation by transaction Ti on a variable Z, wi(Z) denotes a write operation by Ti on a variable Z and ai denotes an abort by transaction Ti .
Which one of the following statements about the above schedule is TRUE?
Step 1. T acquires exclusive locks to $${{O_1},...,{O_k}}$$ in increasing order of their
addresses.
Step 2. The required operations are performed.
Step 3. All locks are released.
This protocol will
(start, $$T4$$); (write, $$T4, y, 2, 3$$); (start, $$T1$$); (commit, $$T4$$); (write, $$T1, z, 5, 7$$);
(checkpoint);
(start, $$T2$$); (write, $$T2, x, 1, 9$$); (commit, $$T2$$); (start, $$T3$$), (write, $$T3, z, 7, 2$$);
If a crash happens now and the system tries to recovver using both undo and redo operations, what are the contents of the undo list and the redo list?