Discuss the final result of the different schedules in Figure 21.3 (a) and (b), where M = 2 and N = 2, with respect to the following questions. Does adding the above condition change the final outcome? Does the outcome obey the implied consistency rule (that the capacity of X is 90)?

Question

Change transaction T 2 in Figure 21.2b to read:
read_item(X);
X:= X+M;
if X > 90 then exit
else write_item(X);

Answer 1

The above condition does not change the final outcome unless the initial value of X > 88.
The outcome, however, does obey the implied consistency rule that X < 90, since the value of X is not updated if it becomes greater than 90.