Cap Theorem easy
How is 'Availability' defined in the context of CAP?
- A Every request received by a healthy, non-failing node must result in a successful (non-error) response.
- B The system uptime must be verified to exceed the standard 'Five Nines' threshold (99.999%).
- C The data stored in the system must be physically accessible to all authenticated users simultaneously.
- D All primary database clusters must have a hot standby or a recent manual backup available.
Answer: A. Every request received by a healthy, non-failing node must result in a successful (non-error) response.
Availability in the CAP Theorem is a strict requirement: any working node in the cluster must be able to respond to any valid request without returning an error. Notably, this guarantee does not promise that the data returned is the most recent update (which is Consistency)—only that the system remains responsive. The trade-off is between UX (staying online) and data integrity (rejecting stale reads).
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