Give schedules that demonstrate incorrect executions in each of the following situations. For each situation, give a one sentence explanation of why the execution is incorrect (for example, `The balance in the bank account is incorrect because ...?)
(a) Transactions are not isolated
(b) Transactions are not atomic
(a) Transactions are not isolated
Solution:
r1(bal = 10) r2(bal = 10) w1(bal = 110) w2(bal = 15) c1 c2
(b) Transactions are not atomic
Solution:
w1(x = 100) r2(x = 100) w2(y = 100) c2 a1
The second transaction was trying to copy the value of x to y, but it copied a value that
was later rolled back. Thus the rst transaction had an e ect even though it did not
commit.
Computer Science & Information Technology
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