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Azure Cosmos DB

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Globally distributed, multi-model distributed NoSQL database with turnkey multi-region writes and guaranteed single-digit millisecond latency.

DATABASES
•Microsoft Azure

Globally distributed, multi-model distributed NoSQL database with turnkey multi-region writes and guaranteed single-digit millisecond latency.

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GCP ➔ Azure Bridge
Fast-Track Mental Model Translation

Coming from Google Cloud?

Compare with Google Cloud Firestore / Spanner

Cosmos DB matches Firestore for document NoSQL and Spanner for global multi-region active-active writes, while offering multiple APIs (Mongo, Cassandra, Gremlin).

What's Conceptually Identical
  • Fully managed, serverless, horizontally partitioned distributed database.
  • Automatic indexing of all document properties by default.
  • Event streaming via Change Feed (equivalent to Firestore document triggers / BigQuery streams).
Key Architectural Shifts in Azure
  • Consistency: Spanner uses TrueTime hardware clocks for global strong consistency; Cosmos DB offers 5 tunable consistency levels.
  • APIs: Firestore is strictly a document database; Cosmos DB supports NoSQL, MongoDB, Cassandra, Gremlin, and Table.
  • Billing: Firestore bills per document read/write; Cosmos DB bills per Request Unit (RU/s) throughput.
Syntax & Command Translator
Create Account
GCP:gcloud firestore databases create --location=nam5
Azure:az cosmosdb create --name cosmos-prod --resource-group rg-data --locations regionName=eastus isZoneRedundant=True
Add Replication Region
GCP:gcloud spanner instances update inst --config=nam-eur-asia1
Azure:az cosmosdb update --name cosmos-prod --resource-group rg-data --locations regionName=eastus regionName=westeurope

What is Azure Cosmos DB?

Azure Cosmos DB is Microsoft's globally distributed, multi-model database service. Built on an Atom-Record-Sequence (ARS) core engine, it supports multiple wire-protocol APIs (NoSQL/Core, MongoDB, Cassandra, Gremlin, Table) while offering 5 well-defined consistency levels, turnkey multi-region replication, and contractual SLAs for availability, latency, throughput, and consistency.

Decision Guide: When to Choose This Service

When to Use Azure Cosmos DB

Use Azure Cosmos DB for global web/mobile applications requiring active-active writes worldwide, high-throughput IoT telemetry, real-time personalization, and applications needing 99.999% Five-Nines availability with sub-10ms latency SLAs.

When NOT to Use (Recommended Alternatives)

Do NOT use Azure Cosmos DB for complex relational OLTP systems requiring heavy multi-table cross-partition ACID transactions or ad-hoc star-schema analytical warehousing (use Azure SQL or Azure Synapse instead).

Core Architectural Pillars

Turnkey Global Active-Active Writes

Read and write locally in any region with sub-10ms P99 latency and 99.999% availability.

The 5 Consistency Models

Strong, Bounded Staleness, Session (default), Consistent Prefix, and Eventual consistency.

Request Units (RU/s)

Normalized throughput currency; 1 point read of a 1 KB item equals exactly 1 RU.

Partitioning

Logical partitions (max 20 GB) mapped across physical SSD shards (max 50 GB and 10k RU/s).

Change Feed

Continuous, ordered log of document modifications powering event-driven microservices.

Integrated Vector Search

Built-in DiskANN vector indexing for semantic similarity search in generative AI RAG.