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3.2.1. Core Concepts: Global Distribution and Consistency
đŸ’¡ First Principle: Cosmos DB trades simplicity and cost for global reach and performance guarantees—pay for throughput (Request Units), not just storage.
Consistency Models (Critical Exam Topic!)
Cosmos DB offers five consistency levels trading off between latency and consistency:
| Consistency Level | Guarantee | Latency | Use Case |
|---|---|---|---|
| Strong | Linearizable reads | Highest | Financial transactions |
| Bounded Staleness | Reads lag by defined time/versions | High | Need strong but can tolerate lag |
| Session | Consistent within a session | Medium | Most common; great for user sessions |
| Consistent Prefix | No out-of-order reads | Low | Messaging, feeds |
| Eventual | No ordering guarantees | Lowest | Analytics, logs |
Visual: Cosmos DB Global Distribution
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