• University of Washington

• CSE 444

1 Concurrency Control with Locking

1. (20 points)

(a) (5 points) Consider a database with objects X, Y, and Z and assume that there are

two transactions T1 and T2. Transaction T1 reads objects X and Y, writes X, and

commits. Transaction T2 reads objects X and Y, writes object Y. It then reads

objects X and Y again, writes X. Finally, it reads object Z, writes it, and commits.

Give three examples of schedules for the transactions T1 and T2 to illustrate each

of the points below:

1. Your schedule should contain a write-read conflict that causes one of the transactions to perform a dirty read.

2. Your schedule should contain a read-write conflict that causes one of the transactions to encounter an unrepeatable read.

3. Your schedule should contain a write-write conflict that causes a lost update.

In each case, your schedule may contain additional conflicts, but should contain

at least one conflict of the type indicated. (In p