Consistency is a trade-off between how fresh a read is and how fast and available writes are. Cosmos DB offers five levels, and the choice affects which service level agreements apply.
Figure 7.1 lays the five levels out on a single spectrum and shows where the SLA and multi-write-region limits fall.
| Consistency (strongest first) | Write-latency SLA on multi-region accounts? |
|---|---|
| Strong | No (a write must commit in every region) |
| Bounded staleness | Yes (the strongest level with this SLA) |
| Session, Consistent prefix, Eventual | Yes |
- Single-region accounts get the latency, throughput, consistency and availability SLA at every consistency level.
- Accounts configured with multiple write regions cannot use Strong consistency at all; bounded staleness works best for single-write-region accounts that span two or more regions.