- A
During a network partition, the system can maintain both consistency and availability.
Why wrong: According to the CAP theorem, during a partition, a distributed system must choose between consistency and availability; it cannot provide both.
- B
When a network partition occurs, a distributed system must choose between providing consistency and providing availability.
This is the core trade-off of the CAP theorem: during a partition, you must sacrifice either consistency (to stay available) or availability (to remain consistent).
- C
Partition tolerance is an optional property and can be sacrificed to achieve both consistency and availability.
Why wrong: In distributed systems, partitions are inevitable; therefore, partition tolerance is a requirement, not optional. Sacrificing it would mean the system stops when a partition occurs.
- D
Availability guarantees that every read returns the most recent write.
Why wrong: Availability in CAP means every request gets a response (not an error), but that response may not contain the latest write. The property that ensures the latest write is returned is consistency.
Quick Answer
The answer is that during a network partition, a distributed system must choose between providing consistency and providing availability. This is the core trade-off described by the CAP theorem: when a partition (P) occurs, you cannot guarantee both strong consistency (C) and full availability (A) simultaneously. In your scenario, because the application must remain fully available even during partitions and can tolerate stale reads, it sacrifices strong consistency for eventual consistency, which is exactly what the theorem dictates. On the Microsoft Azure Data Fundamentals DP-900 exam, this concept tests your understanding of how NoSQL databases like Cosmos DB handle partition tolerance, often with a trap that suggests you can have all three guarantees at once. Remember the mnemonic: when the network splits, pick two—but during a partition, you only get to pick one between C and A.
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 financial services company is evaluating distributed NoSQL databases for a new application that must remain fully available even during network partitions. The application can tolerate stale reads for some types of queries. Which statement accurately describes the trade-off described by the CAP theorem in this context?
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
When a network partition occurs, a distributed system must choose between providing consistency and providing availability.
The CAP theorem states that during a network partition (P), a distributed system must choose between consistency (C) and availability (A). Since the application requires full availability even during partitions, it must sacrifice strong consistency in favor of eventual consistency, which tolerates stale reads. Option B correctly captures this fundamental trade-off.
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.
- ✗
During a network partition, the system can maintain both consistency and availability.
Why it's wrong here
According to the CAP theorem, during a partition, a distributed system must choose between consistency and availability; it cannot provide both.
- ✓
When a network partition occurs, a distributed system must choose between providing consistency and providing availability.
Why this is correct
This is the core trade-off of the CAP theorem: during a partition, you must sacrifice either consistency (to stay available) or availability (to remain consistent).
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Partition tolerance is an optional property and can be sacrificed to achieve both consistency and availability.
Why it's wrong here
In distributed systems, partitions are inevitable; therefore, partition tolerance is a requirement, not optional. Sacrificing it would mean the system stops when a partition occurs.
- ✗
Availability guarantees that every read returns the most recent write.
Why it's wrong here
Availability in CAP means every request gets a response (not an error), but that response may not contain the latest write. The property that ensures the latest write is returned is consistency.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'availability' with 'consistency' or assume that partition tolerance can be sacrificed, when in fact the CAP theorem requires that partition tolerance be a given in any distributed system, and the real choice is between consistency and availability during a partition.
Detailed technical explanation
How to think about this question
Under the hood, when a network partition occurs, nodes in different partitions cannot communicate. A system that chooses availability (AP) will respond to reads from any partition, potentially returning stale data, while a system that chooses consistency (CP) will block or reject reads until the partition heals. In practice, Apache Cassandra is an example of an AP system that uses eventual consistency and last-write-wins conflict resolution, while HBase is a CP system that uses ZooKeeper to enforce strong consistency.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
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FAQ
Questions learners often ask
What does this DP-900 question test?
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: When a network partition occurs, a distributed system must choose between providing consistency and providing availability. — The CAP theorem states that during a network partition (P), a distributed system must choose between consistency (C) and availability (A). Since the application requires full availability even during partitions, it must sacrifice strong consistency in favor of eventual consistency, which tolerates stale reads. Option B correctly captures this fundamental trade-off.
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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Last reviewed: Jun 11, 2026
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