Apply CAP and quorum reasoning
Make the consistency and availability trade-off concrete during a partition.
- State CAP precisely and calculate simple read/write quorum overlap.
CAP applies when a network partition prevents nodes from communicating: a system must choose whether to reject or delay some requests to preserve a single-copy consistency guarantee, or answer requests on both sides and risk divergent results. Partition tolerance is a practical condition for networked systems, not a feature you can switch off. Quorums offer a related tool: with N replicas, read quorum R and write quorum W overlap when R + W > N, assuming the protocol and failure model support that guarantee.
1replicas = 3
2read_quorum = 2
3write_quorum = 2
4print(read_quorum + write_quorum > replicas)True
The arithmetic shows overlap, not a complete consistency proof. Real guarantees depend on versions, leader rules, concurrent writes, membership changes, and which failures the protocol tolerates.
Key takeaways
CAP is a choice made during a partition, not a universal label for normal operation.
Quorum overlap is useful arithmetic, not a complete proof.
State which reads and writes your consistency claim covers.
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