DP-900 Describe core data concepts Practice Question
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?
⚠ Common exam trap
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.
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.
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
This option directly contradicts the CAP theorem's impossibility result: a partition exists precisely when some nodes cannot receive messages from others, so any write accepted on one side is invisible to the other. If the system insists on consistency by rejecting reads on one side, it is unavailable there; if it allows reads to proceed, those reads can miss the latest write. Consequently, during a partition the two properties are mutually exclusive, and no system can deliver both simultaneously.
When this WOULD be correct
This option would be correct in a scenario where the system is not subject to network partitions (e.g., a single-node database or a system that guarantees no partitions), allowing it to provide both consistency and availability.
- ✓
When a network partition occurs, a distributed system must choose between providing consistency and providing availability.
Why this is correct
The CAP theorem formalizes the inherent trade-off of distributed systems during a network partition: when nodes cannot communicate, there is no way to atomically update all replicas and still respond to every client request. To preserve consistency (every read reflects the latest write), a system must refuse requests from nodes that cannot confirm the newest state, sacrificing availability. To preserve availability, nodes must answer requests using only local data, which may be stale, thus sacrificing consistency. Thus the theorem forces an explicit choice once a partition occurs.
- ✗
Partition tolerance is an optional property and can be sacrificed to achieve both consistency and availability.
Why it's wrong here
Partition tolerance cannot be treated as optional in real distributed systems because network partitions are inevitable—links fail, packets are dropped, and nodes crash. The CAP theorem's two-of-three framing is theoretical; in practice you must always preserve P, otherwise the system would be forced to shut down or halt all operations whenever communication breaks. Sacrificing partition tolerance to achieve both consistency and availability is only possible in an idealized, non-partitioned environment, which does not exist in production.
When this WOULD be correct
In a scenario where the question explicitly states that the system is not distributed (e.g., a single-node database) or where the application can tolerate network partitions by design (e.g., using a consensus algorithm that sacrifices availability), then sacrificing partition tolerance could be considered to achieve both consistency and availability.
- ✗
Availability guarantees that every read returns the most recent write.
Why it's wrong here
This statement confuses availability with consistency. In the CAP model, availability means that every request eventually receives a response, even if that response is based on stale data or indicates the server cannot reach a quorum; it does not guarantee the response contains the most recent write. The guarantee that every read returns the most recent write is the definition of linearizable consistency, not availability. A system can be highly available while serving outdated values during a partition.
When this WOULD be correct
In a question asking about the definition of strong consistency in a distributed database, where the requirement is that every read returns the most recent write, this statement would be correct.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The DP-900 exam frequently reuses these exact scenarios with slightly different constraints.
✓When a network partition occurs, a distributed system must choose between providing consistency and providing availability.Correct answer▾
Why this is correct
The CAP theorem formalizes the inherent trade-off of distributed systems during a network partition: when nodes cannot communicate, there is no way to atomically update all replicas and still respond to every client request. To preserve consistency (every read reflects the latest write), a system must refuse requests from nodes that cannot confirm the newest state, sacrificing availability. To preserve availability, nodes must answer requests using only local data, which may be stale, thus sacrificing consistency. Thus the theorem forces an explicit choice once a partition occurs.
✗During a network partition, the system can maintain both consistency and availability.Wrong answer — click to see why▾
Why this is wrong here
The CAP theorem states that during a network partition, a distributed system must choose between consistency and availability; it cannot maintain both simultaneously, making this statement false.
★ When this WOULD be the correct answer
This option would be correct in a scenario where the system is not subject to network partitions (e.g., a single-node database or a system that guarantees no partitions), allowing it to provide both consistency and availability.
Why candidates choose this
Candidates may mistakenly believe that modern distributed systems can achieve both consistency and availability under all conditions, overlooking the fundamental trade-off imposed by the CAP theorem during partitions.
✗Partition tolerance is an optional property and can be sacrificed to achieve both consistency and availability.Wrong answer — click to see why▾
Why this is wrong here
Partition tolerance is not optional in distributed systems; the CAP theorem states that during a network partition, you must choose between consistency and availability, but partition tolerance itself is a requirement for distributed systems, not a trade-off.
★ When this WOULD be the correct answer
In a scenario where the question explicitly states that the system is not distributed (e.g., a single-node database) or where the application can tolerate network partitions by design (e.g., using a consensus algorithm that sacrifices availability), then sacrificing partition tolerance could be considered to achieve both consistency and availability.
Why candidates choose this
Candidates may misinterpret the CAP theorem as allowing a choice to drop partition tolerance entirely, rather than understanding that partition tolerance is a fundamental requirement for distributed systems, and the trade-off is between consistency and availability during a partition.
✗Availability guarantees that every read returns the most recent write.Wrong answer — click to see why▾
Why this is wrong here
Availability in the CAP theorem means every request receives a response, but not necessarily the most recent write. Option D incorrectly defines availability as returning the most recent write, which is actually a consistency guarantee.
★ When this WOULD be the correct answer
In a question asking about the definition of strong consistency in a distributed database, where the requirement is that every read returns the most recent write, this statement would be correct.
Why candidates choose this
Candidates often conflate availability with consistency, assuming that an available system always returns the latest data, not realizing that availability only guarantees a response, not its freshness.
Analysis generated from the official DP-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DP-900 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DP-900 exam.