Quorum
Quorum requires operations to be acknowledged by a majority of nodes, guaranteeing consistency and availability despite minority failures.
Purpose
To design read/write quorums balancing consistency against performance; the core mechanism of Dynamo-style systems.
Mechanism
With N replicas, write quorum W and read quorum R must satisfy W+R>N to guarantee read/write intersection. Commonly W=R=ceil((N+1)/2). Strongly consistent reads use R=N/2+1; low-latency reads use R=1 (sacrificing consistency).
Use cases
- Dynamo replication design
- Read/write trade-offs
- Fault-tolerant consistency