OceanBase uses Paxos quorums per log stream. Multi-region layouts must place enough replicas across zones so a region loss still forms a majority. Witness or log-only replicas can reduce cross-region data copies when official topology options support them for your edition.
Multi-region OceanBase clusters depend on quorum math at the log stream level. A region loss must still leave a Paxos majority for each active stream.
Quorum basics
- Full replicas: Hold tablet data and participate in Paxos.
- Witness / log replicas (when supported for your topology): Reduce full copies while participating in consensus.
- Majority rule: Writes need a majority of replicas in the Paxos group for each log stream.
Two-region vs three-region
| Layout | Trade-off |
|---|---|
| Two regions + witness | Lower cost; witness placement is critical |
| Three full regions | Higher fault tolerance; more cross-region replication lag |
Measure replication lag and failover time in your network; do not copy reference topologies without validation.
Design checklist
- Map zones to failure domains (AZ, data center, region).
- Set locality so each log stream has the intended replica count per zone.
- Run failover drills after any locality change.
- Document RPO if asynchronous cross-region paths exist outside Paxos.
Common mistakes
- Equal replica counts without witness when cross-region bandwidth is limited.
- Application timeouts shorter than measured failover duration.
- Changing locality without rehearsing leader elections.