CAP theorem: why distributed systems must trade consistency against availability

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Distributed systems cannot simultaneously guarantee consistency, availability, and partition tolerance, a limit described by computer scientist Eric Brewer in the CAP theorem. Consistency means every node returns the same, most recent data, while availability means every request gets a response even if the data may be stale. Because network partitions are unavoidable in modern cloud environments, developers must generally choose between consistency and availability when a partition occurs. The article illustrates this with an ATM example, where a consistent system may reject withdrawals while an available one may allow overdrafts. It notes that banking and inventory systems favor consistency, whereas social networks and content platforms favor availability.

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