Under a network partition you must choose availability or consistency (CAP). Even without partitions, you trade latency against consistency (PACELC).
Key ideas
- Strong consistency: every read sees the latest write — simpler reasoning, higher latency/coordination.
- Eventual consistency: replicas converge over time — higher availability, must tolerate stale reads.
- Pick per-operation: a bank balance wants strong; a like-count tolerates eventual.
Compare
| Model | Good for |
|---|---|
| Strong | Money, inventory, uniqueness |
| Eventual | Feeds, counters, analytics |