Replication, Consistency, and Time
Once data has two copies, they can disagree. See what each replication scheme costs, what the models between strong and eventual promise, and when clocks lie.
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CAP Theorem
CAP forbids perfect consistency with perfect availability during a partition — a narrower claim than the “pick two of three” framing suggests.
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PACELC
PACELC adds what CAP omits: when there is no partition, you are still trading latency against consistency — and that is the trade you live with daily.
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Linearizability
Linearizability preserves real-time order between non-overlapping operations. Concurrent reads and writes can be ordered within their execution intervals.