cosmosdb

Azure Cosmos DB

Cosmos DB is Azure's planetary-scale database. It supports multiple APIs: NoSQL (Core/JSON), MongoDB, PostgreSQL, Cassandra, Gremlin (Graph), and Table.

When to Use

• Global Enterprise Applications on Azure: Fully managed NoSQL database with turnkey multi-region replication and single-digit millisecond latency SLAs.
• Multi-Model API Compatibility: Using existing MongoDB, Apache Cassandra, Gremlin (Graph), or PostgreSQL skills via native Cosmos DB APIs.
• Dynamic Scale & Autoscale Request Units (RU/s): Applications with seasonal traffic spikes scaling compute and throughput instantly.
• Guaranteed Consistency Options: Tuning consistency across 5 distinct levels (Strong, Bounded Staleness, Session, Consistent Prefix, Eventual).

Quick Start

Container container = database.GetContainer("Items");

Item item = new Item
{
    Id = "1",
    Category = "Personal",
    Name = "Groceries"
};

await container.CreateItemAsync(item, new PartitionKey(item.Category));

Core Concepts

Request Units (RU/s) Throughput Currency

Throughput is normalized into Request Units; a 1KB point read costs 1 RU:

// Azure Cosmos DB Node.js SDK (NoSQL API)
import { CosmosClient } from "@azure/cosmos";

const client = new CosmosClient({
  endpoint: process.env.COSMOS_ENDPOINT!,
  key: process.env.COSMOS_KEY!,
});

const container = client.database("CommerceDb").container("Orders");

// Point read with exact partition key (Cost: 1 RU)
const { resource, requestCharge } = await container
  .item("order_415", "customer_99")
  .read();
console.log(`Retrieved order. Request Charge: ${requestCharge} RUs`);

Partition Key Selection (Physical vs Logical Partitions)

The partition key determines how items are distributed across physical servers; high-cardinality keys ensure even distribution:

// Items must include the partition key property
{
  "id": "order_415",
  "customerId": "customer_99", // Partition Key
  "totalAmount": 149.5,
  "orderStatus": "SHIPPED"
}