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FC0-U71 Practice Question: A banking transaction transfers money from…
A banking transaction transfers money from savings to checking. The system updates the savings balance, then the power fails before the checking balance is updated. Which ACID property is violated?
⚠ Common exam trap
Candidates often confuse atomicity with consistency, thinking a partial update violates consistency first, but the core issue is that the transaction did not complete as an atomic unit, which is the direct violation of atomicity.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
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Atomicity
Atomicity ensures that a transaction is treated as a single, indivisible unit of work. In this scenario, the transfer operation consists of two steps: deducting from savings and crediting to checking. Because the power failure occurs after the savings balance is updated but before the checking balance is updated, the transaction is left partially completed, violating atomicity. The system must either complete both steps or roll back the first step to maintain atomicity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Atomicity
Why this is correct
Atomicity guarantees that a transaction is treated as a single all-or-nothing unit. Here the savings debit committed while the checking credit never occurred, leaving the database in a partial state, which is precisely the inconsistency atomicity prevents.
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Isolation
Why it's wrong here
Isolation governs concurrent transactions interfering with each other, not a single transaction interrupted by power loss. Isolation is the correct property to cite when dirty reads or lost updates occur between simultaneous transactions, not when a partial write leaves data inconsistent after a crash.
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Durability
Why it's wrong here
Durability guarantees committed data survives failure; here the transaction never committed, so nothing was promised to persist. Durability is the correct property when acknowledged writes are lost after a crash, not when an uncommitted partial update leaves the database inconsistent.
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Consistency
Why it's wrong here
Consistency concerns rules and constraints holding before and after a transaction, not recovery of an interrupted partial write. Consistency is the correct property when a constraint or invariant is broken by a completed transaction, not when power loss leaves one balance updated and the other not.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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