Two concurrent executing transactions T1 and T2 are allowed to update same…
2025
Two concurrent executing transactions T1 and T2 are allowed to update same stock item say ‘A’ in an uncontrolled manner. In such scenario. Following problems may occur:
(a) Dirty read problem
(b) Lost update problem
(c) Transaction failure
(d) Inconsistent database state
Which of the following option is correct if database system has no concurrency module and allows concurrent execution of above two transactions? [Asked in L&T Infotech (LTI) 2021]
[ This test belongs to Paid Members of KNOWLEDGE GATE ]
&T
- A.
(a), (b) and (c) only
- B.
(c) and (d) only
- C.
(a) and (b) only
- D.
(a), (b) and (d) only
Attempted by 135 students.
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Correct answer: D
Ans : D
Solution
Problems that can occur during concurrent execution of two transactions in an uncontrolled manner:
a) Lost update problem: Occurs when two transactions access the same database item and their operations are interleaved, causing one update to overwrite another, resulting in incorrect data.
b) Dirty read problem: Occurs when a transaction reads data that has been modified by another transaction but not yet committed. Since the update may be rolled back, the reading transaction sees inconsistent or invalid data.
c) Inconsistent database state: Occurs when a transaction reads multiple values, and another transaction modifies some of those values during the first transaction's execution. This leads to incorrect results, such as an incorrect aggregate calculation.
Note: Transaction failure is not a concurrency problem; it refers to a transaction failing due to system errors or logical issues, not due to interference between concurrent transactions.