In the context of concurrency control, a given pair of operations in a…
2020
In the context of concurrency control, a given pair of operations in a schedule is called conflict schedule if
(A) At least one of the operations is write operation
(B) Both the operations are performed on the same data item
(C) Both the operations are performed by different transactions
(D) Both the operations are performed on different data items
Choose the correct answer from the options given below:
- A.
(A) and (B) Only
- B.
(A), (B) and (C) Only
- C.
(A), (C) and (D) Only
- D.
(C) and (D) Only
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Correct answer: B
Definition of conflicting operations: Two operations in a schedule conflict only when all of the following are true.
They operate on the same data item.
They are performed by different transactions.
At least one of the two operations is a write.
Therefore, the correct choice must list these three conditions: same data item, different transactions, and at least one write. Any answer that replaces "same data item" with "different data items" or omits the write requirement is incorrect.
Why the other statements fail:
If operations touch different data items, they cannot interfere with each other and so do not conflict.
If both operations are reads (no writes), they do not conflict even if they are on the same item and by different transactions.
Short examples:
Conflict example: Transaction 1 reads X and Transaction 2 writes X — these operations conflict.
No-conflict example: Transaction 1 reads X and Transaction 2 reads X — two reads do not conflict.
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