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Study Stuff for MCA Examinations - NIMCET
Previous Year Question (PYQs)
Two concurrent executing transactions $T_1$ and $T_2$ 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?
Solution
If two transactions update the same data item without concurrency control, then many problems may occur.
Dirty read problem can occur when one transaction reads uncommitted data of another transaction.
Lost update problem can occur when one transaction update is overwritten by another transaction.
Inconsistent database state can occur because uncontrolled concurrent execution may violate consistency.
But transaction failure is not necessarily due to concurrency control absence.
So, correct problems are:
(a), (b) and (d)
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