What does the CAP theorem state about distributed systems under network partitions?

• A. CAP states a system can guarantee all three properties under all conditions.
• B. In a partition, a system can guarantee at most two of consistency, availability, partition tolerance.
• C. CAP is about optimizing transaction throughput.
• D. CAP suggests that partition tolerance is optional.

Answer: (B)

The key idea here is that in a distributed system, a network partition creates a fundamental trade-off among three properties: consistency, availability, and partition tolerance. Partition tolerance means the system can keep operating even if some nodes can’t communicate with others. Once a partition occurs, you can’t satisfy all three at once. You must choose between keeping consistency (all reads see the same data) or keeping availability (the system responds to requests promptly). In other words, during a partition you can guarantee at most two of the three properties, which is why systems are often described as CP (consistency and partition tolerance) or AP (availability and partition tolerance) depending on which trade-off they prioritize.