Standard replication: one primary accepts writes. Multi-master allows writes to any node.
Benefits:
- Write availability if one master fails
- Lower latency (write to nearest master)
- No single write bottleneck
Challenges:
- Conflict resolution (both masters update same row)
- Complexity
- Data divergence risk
Conflict resolution:
- Last-write-wins (simple, loses data)
- Application-level merge (complex, accurate)
- CRDTs (automatic merge for certain data types)
Multi-master is complex. Use single-master with failover unless you truly need multi-region writes.