DP-900 Describe core data concepts Practice Question
This DP-900 practice question tests your understanding of describe core data concepts. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A banking system processes a money transfer between two accounts. The system is designed so that after the transaction is committed, the results are permanently saved and survive any subsequent system failure, such as a power outage. Which ACID property ensures this behavior?
Correct. Durability guarantees that committed changes are saved permanently, surviving failures.
B
Atomicity
Why wrong: Incorrect. Atomicity ensures the transaction completes entirely or not at all, not that it survives failures after commit.
C
Consistency
Why wrong: Incorrect. Consistency ensures that the database remains in a valid state before and after the transaction, but does not address persistence after failure.
D
Isolation
Why wrong: Incorrect. Isolation deals with the visibility of uncommitted changes to other transactions, not with durability of committed data.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Durability
Durability ensures that once a transaction is committed, its changes are permanently stored and survive system failures, such as power outages or crashes. In this banking scenario, the money transfer results are written to non-volatile storage (e.g., disk) via a write-ahead log, guaranteeing that the committed state is recoverable even after a restart.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Durability
Why this is correct
Correct. Durability guarantees that committed changes are saved permanently, surviving failures.
Related concept
Read the scenario before looking for a memorised answer.
✗
Atomicity
Why it's wrong here
Incorrect. Atomicity ensures the transaction completes entirely or not at all, not that it survives failures after commit.
✗
Consistency
Why it's wrong here
Incorrect. Consistency ensures that the database remains in a valid state before and after the transaction, but does not address persistence after failure.
✗
Isolation
Why it's wrong here
Incorrect. Isolation deals with the visibility of uncommitted changes to other transactions, not with durability of committed data.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse durability with atomicity, thinking that 'surviving failures' means the transaction either completes fully or not at all, but atomicity handles the rollback of partial transactions, not the persistence of committed ones.
Detailed technical explanation
How to think about this question
Under the hood, durability is typically implemented using a transaction log (e.g., SQL Server's transaction log or PostgreSQL's WAL) where every committed change is written to disk before the transaction is acknowledged. In the event of a power outage, the database engine replays the log during recovery to restore any committed transactions that were not yet flushed to the data files. A real-world scenario is a bank transfer where the debit and credit are logged; if the system crashes after the commit but before the data pages are written, the log ensures the transfer is not lost.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-900 question in full detail.
Describe core data concepts — This question tests Describe core data concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Durability — Durability ensures that once a transaction is committed, its changes are permanently stored and survive system failures, such as power outages or crashes. In this banking scenario, the money transfer results are written to non-volatile storage (e.g., disk) via a write-ahead log, guaranteeing that the committed state is recoverable even after a restart.
What should I do if I get this DP-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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