Quorum-Based Replication
-
Quorum Definition:
- Based on majority instead of requiring all nodes
-
Replication Mechanism:
- Quorum Replication: Pull-based
- Leader handles all write operations
- Followers make fetch requests to the leader (pull-based)
-
Commit Process:
- The leader commits a write after receiving acknowledgments (acks) from a majority of followers, including itself
- Ack: Request for the next write from a follower
-
Trade-offs:
- Balances between replication latency and delivery guarantee
-
ISR Concept:
- New concept of ISR (In-Sync Replicas) introduced for controller replicas
-
Protocol Implementation:
- Implemented by the Raft protocol
To tolerate N failures, a quorum need to have
2N + 1 replicas