GATE CSE 2026 | Set 2 | Question: 10

Question

Consider concurrent execution of two transactions $T 1$ and $T 2$ in a DBMS, both of which access a data object $A$. For these two transactions to not conflict on $A$, which one of the following statements must be true?

• A. Both $T 1$ and $T 2$ only read $A$
• B. $T 1$ reads $A$ and $T 2$ writes $A$
• C. $T 1$ writes $A$ and $T 2$ reads $A$
• D. Both $T 1$ and $T 2$ write $A$

Answer 1

Answer: Option A

In a DBMS, two operations on the same data object Q are said to be in conflict if at least one of them is a Write operation.

Conflict Conditions

For two transactions T1 and T2 accessing the same data object Q are said to be in conflict if at least one of them is a Write operation.

1. Read-Read (R-R): No Conflict. Both transactions are only viewing the data; the state of $Q$ remains unchanged.

2. Read-Write (R-W): Conflict. One transaction reads while the other updates, leading to potential inconsistency.

3. Write-Read (W-R): Conflict. Known as a "Dirty Read" if the write hasn't been committed.

4. Write-Write (W-W): Conflict. Known as a "Blind Write" or "Lost Update" problem.

Therefore, for T1 and T2 to not conflict, the only valid scenario is when both T1 and T2 only read Q.

https://www.geeksforgeeks.org/dbms/concurrency-control-in-dbms/ 

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Answer 2

for more -> https://cstaleem.com/conflict-in-dbms

Answer 3

Although I am not a Database Expert But I shall try to Explain in a Simple Trick.

Always Remember : Write is the main culprit. It creates Conflicts.

Then : 

Option B : T1 reads A and T2 writes A  = CONFLICT

Option C : T1 writes A and T2 reads A   = CONFLICT

Option D : Both T1 and T2 write A   = CONFLICT

Hence, 

Option A = Correct

 

 

 

 

Answer 4

The question says that T1 and T2 accessed data item A. And we want that both the transactions should not conflict with each other while performing any operation on A. And we have to find out at what situation it will be possible that both the transactions will not conflict with each other while perfoming any operation on it.

 

So, conflict can occur through the following pairs :

1. Read-After-Write (Occuring in Option C)

2. Write-After-Read (Occuring in Option B) 

3. Write-After-Write (Occuring in Option D)  

Only in Read-After-Read pair, conflict is not possible (Occuring in Option A)  

Therefore, the correct option is A.

Answer 5

There will be no conflict between the transactions if they only read the data; if anyone of it performs write action, the conflict will occur, hence following is the correct answer.

1. Both T1 and T2 only read A