Why it matters

Understanding quorum shapes reasoning about distributed data consistency. Foundational for eventually-consistent systems.

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The architecture

N: total replicas.

W: write quorum. Writes must reach W replicas.

R: read quorum. Reads consult R replicas.

Quorum settingsN replicastotalW write quorummust acknowledgeR read quorummust respondR + W > N gives strong consistency; R + W ≤ N eventual consistency
Quorum semantics.
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How it works end to end

Strong consistency: R + W > N ensures reads see committed writes.

Common: N=3, R=2, W=2. Strong consistency, tolerates 1 failure.

Read-optimized: R=1, W=N. Fast reads, slow writes.

Write-optimized: W=1, R=N. Fast writes, slow reads.