Distributed Systems Lab
Eleven ideas that only matter once you have more than one machine.
Quorum
How many votes make it official.
N replicas, W nodes that must ack a write, R nodes you read from. Strong consistency needs W + R > N — that guarantees every read overlaps with the last write.
N — total replicas5
W — write quorum3
R — read quorum2
W + R = 5 ≤ N = 5
Reads may return stale data
There's a possible read set that misses every replica holding the latest write. Lower latency, weaker guarantees.