COSC 471/571    quiz 11/15    Name:

1. Consider this schedule. Give the corresponding log.  No checkpointing.

The data elements x, y, and z are all value 0 in the database files at the start
of the schedule.

The log entries are of the form:
<T# starts>
<T# commits>
<T#, x, old_value, new_value>

Schedule:
time      T1                        T2
=====    ===============           ====================
1         r(x)
2         r(y)
3                                   r(z)
4         x += 10
5                                   z = 15
6         w(x)
7         y = x
8                                   w(z)
9         w(y)
10                                  r(x)
11                                  r(y)
12        commit
13                                  x = z
14                                  y = z * 1000
14                                  w(x)
15                                  w(y)
16                                  commit




































2. The schedule is repeated here with interleaving blank spaces.
Show where the programmer of T1 and T2 should have inserted appropriate
locking and unlocking commands to implement two phase locking.

The locking/unlocking commands are of the form:
r-lock(x)     read lock on x
w-lock(y)     write lock on y
unlock(y)     release lock on y
unlock()      release all locks

Schedule:
time      T1                        T2
=====    ===============           ====================

1         r(x)

2         r(y)

3                                   r(z)

4         x += 10

5                                   z = 15

6         w(x)

7         y = x

8                                   w(z)

9         w(y)

10                                  r(x)

11                                  r(y)

12        commit

13                                  x = z

14                                  y = z * 1000

14                                  w(x)

15                                  w(y)

16                                  commit