No Leader At All
In a leaderless system any replica can accept writes, unlike leader based replication where one node is authoritative. Dynamo style stores work this way. Correctness depends on requiring enough replicas to participate in each operation.
The Quorum Condition
With a replication factor of N, a write must be acknowledged by W replicas and a read must gather from R replicas. The key rule is that W plus R must exceed N. This forces the read set and the write set to overlap by at least one replica, so a read always touches at least one node holding the latest write.
Choosing W and R
- Favoring writes uses a small W and large R, so writes are fast but reads are slower.
- Favoring reads does the opposite.
- A common balanced choice sets both to a strict majority.
What Quorums Do Not Solve
Even with overlap, concurrent writes can produce conflicting versions, and a slow or failed node can leave some replicas stale until repair mechanisms catch up. Quorums give a baseline, not perfection.
Key idea
Leaderless replication relies on overlapping quorums, where W plus R exceeding N guarantees every read touches a replica with the latest write, though conflicts and stale replicas still need repair.