GATE CS 2025 Set 1 Q.15: Transactions, Serializability and Concurrency Control

A schedule of three database transactions $T_1$ , $T_2$ , and $T_3$ is shown. $R_i(A)$ and $W_i(A)$ denote read and write of data item $A$ by transaction $T_i$ , $i = 1, 2, 3$ . The transaction $T_1$ aborts at the end. Which other transaction(s) will be required to be rolled back?

R_1(X)\; W_1(Y)\; R_2(X)\; R_2(Y)\; R_3(Y)\; \text{ABORT}(T_1)

Only $T_2$

Only $T_3$

Both $T_2$ and $T_3$

Neither $T_2$ nor $T_3$

Official answer and solution

Official answer: C
From: Official GATE 2025 answer key

Solution

Identify which transactions read an uncommitted data item written by $T_1$ (dirty reads).

In the given schedule:

$T_1$ writes data item $Y$ via $W_1(Y)$ .
Before $T_1$ commits or aborts, both $T_2$ (via $R_2(Y)$ ) and $T_3$ (via $R_3(Y)$ ) read the uncommitted value of $Y$ written by $T_1$ (a dirty read).
When $T_1$ aborts at the end, the value of $Y$ written by $T_1$ becomes invalid, so both $T_2$ and $T_3$ must be rolled back (cascading rollback).

Final answer

Option (C)

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2025 Computer Science and Information Technology - Session 1 (CS1)
Question: 15 of 65
Section: Computer Science and Information Technology

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