Quorum
A quorum is how many replicas must respond for an operation to count — and overlapping read and write sets is what lets a read see the last write.
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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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Replication and Consistency: Living With Copies That Disagree
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.