CAP Theorem Vocabulary

1. In the CAP theorem, a system guarantees that every read receives the most recent write or an error — never stale data. Which CAP property does this describe?

Availability Partition tolerance Consistency

2. An engineer says: 'Our system favours CP — we sacrifice availability during a network partition.' What does this mean in practice?

The system serves stale data but remains online during partitions The system refuses requests it cannot serve with consistent data — it returns errors or timeouts during partitions rather than risk serving stale data The system shuts down entirely when a partition occurs

3. The system continues to serve all requests and return responses, even if some nodes cannot communicate with each other. Which CAP property does this prioritise?

Consistency Availability Durability

4. PACELC extends the CAP theorem by considering a trade-off that also applies when the system is operating normally, without any partition. What trade-off does PACELC add?

Throughput vs. storage cost Latency vs. consistency — even without a partition, choosing stronger consistency requires extra coordination round-trips, increasing latency Partition recovery speed vs. node count

5. A team describes their database: 'When a partition occurs, nodes on each side continue accepting writes independently. After the partition heals, conflicts are resolved by last-write-wins.' What CAP category does this describe?

CP — consistency over availability AP — availability over consistency, with eventual consistency after healing CA — both consistency and availability guaranteed

Vocabulary Reference

Term	Meaning
consistency (CAP)	Every read returns the most recent write or an error — never stale data.
availability (CAP)	Every request receives a response (not necessarily the latest data).
partition tolerance	The system continues operating even when messages between nodes are lost or delayed.
CP system	Sacrifices availability during a network partition to preserve consistency; requests may timeout or error.
AP system	Remains available during partitions by serving potentially stale data; consistency is eventual.
PACELC	Extension to CAP: during a Partition choose A or C; Else choose Latency or Consistency.

Vocabulary Reference

Exercise complete!