- A
Consistency and Partition Tolerance
Why wrong: This would mean the system sacrifices Availability during a partition, which contradicts the requirement that the service must remain highly available and accept writes.
- B
Availability and Partition Tolerance
The system is designed to remain available (accept writes) even during network partitions, sacrificing immediate consistency (stale data is acceptable). This is a classic 'AP' system under the CAP theorem.
- C
Consistency and Availability
If a system prioritizes both Consistency and Availability, it cannot tolerate network partitions. Since partitions are inevitable, this combination is not achievable in practice.
- D
Durability and Partition Tolerance
Why wrong: Durability is not one of the three properties in the CAP theorem. The CAP theorem addresses Consistency, Availability, and Partition Tolerance.
Quick Answer
The answer is Availability and Partition Tolerance. This is correct because the CAP theorem states that during a network partition, a distributed system must choose between Consistency and Availability; here, the system continues accepting writes and remains operational despite the partition, prioritizing Availability, while Partition Tolerance is inherently required since the system functions across data centers even when network splits occur. The business accepts slightly outdated inventory counts, meaning it sacrifices strong Consistency for eventual consistency, which aligns with an AP (Availability and Partition Tolerance) system. On the Microsoft Azure Data Fundamentals DP-900 exam, this scenario tests your understanding of how real-world trade-offs apply to distributed databases like Azure Cosmos DB, where you can configure consistency levels. A common trap is confusing “high availability” with the CAP property of Availability—remember, in CAP, Availability means the system always accepts reads and writes, not just that it stays up. A helpful memory tip: “AP stands for Always Partying” — the system keeps working (Availability) even when the network is broken (Partition Tolerance).
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 global e-commerce platform uses a distributed database for its shopping cart service. The platform must be highly available and continue to accept writes even if network partitions occur between data centers. The business accepts that during a partition, users might see slightly outdated inventory counts, but the service must remain operational. According to the CAP theorem, which two properties is this system prioritizing?
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
Availability and Partition Tolerance
The scenario describes a system that must remain operational and accept writes during network partitions, even if data becomes temporarily inconsistent (stale inventory counts). This prioritizes Availability (the service stays up and accepts writes) and Partition Tolerance (the system continues to function despite network splits). According to the CAP theorem, when a partition occurs, a distributed system must choose between Consistency and Availability; here, the business accepts eventual consistency, so Availability and Partition Tolerance are the chosen properties.
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.
- ✗
Consistency and Partition Tolerance
Why it's wrong here
This would mean the system sacrifices Availability during a partition, which contradicts the requirement that the service must remain highly available and accept writes.
- ✓
Availability and Partition Tolerance
Why this is correct
The system is designed to remain available (accept writes) even during network partitions, sacrificing immediate consistency (stale data is acceptable). This is a classic 'AP' system under the CAP theorem.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Consistency and Availability
Why this is correct
If a system prioritizes both Consistency and Availability, it cannot tolerate network partitions. Since partitions are inevitable, this combination is not achievable in practice.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Durability and Partition Tolerance
Why it's wrong here
Durability is not one of the three properties in the CAP theorem. The CAP theorem addresses Consistency, Availability, and Partition Tolerance.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume 'highly available' automatically means 'Consistency and Availability' (CA), forgetting that the CAP theorem states you cannot have all three during a partition, and the scenario explicitly allows stale data, which sacrifices Consistency for Availability.
Detailed technical explanation
How to think about this question
Under the CAP theorem, during a network partition, a system must choose between CP (Consistency + Partition Tolerance) and AP (Availability + Partition Tolerance). This scenario describes an AP system, often implemented using eventually consistent data stores like Apache Cassandra or DynamoDB with read-repair and hinted handoffs. In practice, the shopping cart service might use multi-region replication with asynchronous updates, where writes are accepted locally and propagated later, allowing the service to remain writable even if data centers are disconnected.
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: Availability and Partition Tolerance — The scenario describes a system that must remain operational and accept writes during network partitions, even if data becomes temporarily inconsistent (stale inventory counts). This prioritizes Availability (the service stays up and accepts writes) and Partition Tolerance (the system continues to function despite network splits). According to the CAP theorem, when a partition occurs, a distributed system must choose between Consistency and Availability; here, the business accepts eventual consistency, so Availability and Partition Tolerance are the chosen properties.
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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