Leaderless Replication
Summary: A replication model where any node can accept writes, and the system does not designate a single node as the leader. Clients often send writes to several nodes in parallel.
Sources: chapter5
Last updated: 2026-04-15
In leaderless replication, also known as Dynamo-style replication, there is no single node that manages writes. Instead, every replica can accept writes from clients directly. This model was popularized by Amazon’s Dynamo system and is used in databases like Riak, Cassandra, and Voldemort (source: chapter5, p. 177).
How it Works
When a client wants to write data, it sends the request to several nodes in parallel. Similarly, when it wants to read data, it sends requests to several nodes. To ensure consistency, leaderless systems rely on quorums (source: chapter5, p. 179).
Quorums
A quorum is the minimum number of nodes that must participate in an operation for it to be considered successful. If there are replicas, and each write is confirmed by nodes, and each read is served by nodes, then as long as , we expect to get an up-to-date value when reading (source: chapter5, p. 179).
Keeping Replicas in Sync
When a node comes back online after being unavailable, it may have missed some writes. Leaderless systems use two mechanisms to catch up:
- read-repair: When a client reads from several nodes and notices that one of them has stale data, it can write the newer value back to that node (source: chapter5, p. 178).
- anti-entropy: A background process that constantly looks for differences in data between replicas and copies any missing data from one replica to another (source: chapter5, p. 179).