What a partition is
A network partition is when links break and nodes split into groups that cannot talk to each other, even though each group is alive. Partitions are not rare; they happen on every large network.
The CAP forcing function
During a partition you cannot have both consistency and availability. You must pick:
- CP reject or block writes on the minority side to stay consistent
- AP keep serving on both sides and reconcile later
This is not a free choice; it follows from the laws of the system.
Detecting partitions
- Heartbeats stop arriving from a group of peers
- Quorum reads or writes start failing
- A node sees itself isolated from the majority
Common strategies
- Quorum majority lets the larger side keep working while the minority steps back
- Fencing tokens stop a stale leader from acting after a split
- Read repair and anti entropy reconcile divergent replicas afterward
A warning
The worst outcome is both sides believing they are authoritative and accepting conflicting writes. That is split brain, and partition handling exists largely to prevent it.
Key idea
A partition splits live nodes into isolated groups, and CAP forces you to sacrifice consistency or availability; quorums and fencing decide which side keeps working.