CAP Theorem

Distributed

CAP Theorem

During a network partition a system must choose between consistency (linearizability) and availability.

Why interviewers ask about it

P is not optional. 'Pick two' is misleading - CAP is a conditional about behaviour during a partition, and most databases are tunable per request.

PACELC

If Partition then Availability or Consistency; Else Latency or Consistency.

Linearizability

Operations appear to take effect instantaneously at a single point between invocation and response - the single-copy illusion.

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