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GATE 2025 CS (CS2) – Question 27

Databases · Transactions and Concurrency Control · 1 mark · Multiple select

An audit of a banking transactions system has found that on an earlier occasion, two joint holders of account $A$ attempted simultaneous transfers of Rs. 10000 each from account $A$ to account $B$. Both transactions read the same value, Rs. 11000, as the initial balance in $A$ and were allowed to go through. $B$ was credited Rs. 10000 twice. $A$ was debited only once and ended up with a balance of Rs. 1000.

Which of the following properties is/are certain to have been violated by the system?

  1. Atomicity
  2. Consistency
  3. Isolation
  4. Durability

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Show answer and explanation

Correct answer: (C) Isolation

Explanation

Both transactions read the same stale balance and one update was overwritten (a lost update). This is a failure of isolation, since the transactions interfered with each other. Each transaction ran to completion, so atomicity and durability were not violated.