azure-cosmosdb

Files (1)

• SKILL.md

SKILL.md (first lines)

## Core Principle

**Choose partition key wisely, design for your access patterns, understand consistency tradeoffs.**

Cosmos DB distributes data across partitions. Your partition key choice determines scalability, performance, and cost. Design for even distribution and query efficiency.

---

## Cosmos DB APIs

| API | Use Case |
|-----|----------|
| **NoSQL (Core)** | Document database, most flexible |
| **MongoDB** | MongoDB wire protocol compatible |
| **PostgreSQL** | Distributed PostgreSQL (Citus) |
| **Apache Cassandra** | Wide-column store |
| **Apache Gremlin** | Graph database |
| **Table** | Key-value (Azure Table Storage compatible) |

This skill focuses on **NoSQL (Core) API** - the most common choice.

---

## Key Concepts

| Concept | Description |
|---------|-------------|
| **Container** | Collection of items (like a table) |
| **Item** | Single document/record (JSON) |
| **Partition Key** | Determines data distribution |
| **Logical Partition** | Items with same partition key |
| **Physical Partition** | Storage unit (max 50GB, 10K RU/s) |
| **RU (Request Unit)** | Throughput currency |

---

## Partition Key Design

### Good Partition Keys
```typescript
// High cardinality, even distribution, used in queries

// E-commerce: userId for user data
{ "id": "order-123", "userId": "user-456", ... }  // PK: /userId

// Multi-tenant: tenantId
{ "id": "doc-1", "tenantId": "tenant-abc", ... }  // PK: /tenantId

// IoT: deviceId for telemetry
{ "id": "reading-1", "deviceId": "device-789", ... }  // PK: /deviceId

// Logs: synthetic key (date + category)
{ "id": "log-1", "partitionKey": "2024-01-15_errors", ... }  // PK: /partitionKey
```

### Hierarchical Partition Keys
```typescript
// For multi-level distribution (e.g., tenant → user)
// Container created with: /tenantId, /userId

{
  "id": "order-123",
  "tenantId": "acme-corp",
  "userId": "user-456",
  "items": [...]
}

// Query within tenant and user efficiently
```

### Bad Partition Keys
```typescript
// Avoid:
// - Low cardinality (status, type, boolean)
// - Monotonically increasing (timestamp, auto-increment)
// - Frequently updated fields
// - Fields not used in queries

// Bad: Only 3 values → hot partitions
{ "status": "pending" | "completed" | "cancelled" }

// Bad: All writes go to latest partition
{ "timestamp": "2024-01-15T10:30:00Z" }
```

---

## SDK Setup (TypeScript)

### Install
```bash
npm install @azure/cosmos
```

### Initialize Client
```typescript
// lib/cosmosdb.ts
import { CosmosClient, Database, Container } from '@azure/cosmos';

const endpoint = process.env.COSMOS_ENDPOINT!;
const key = process.env.COSMOS_KEY!;
const databaseId = process.env.COSMOS_DATABASE!;

const client = new CosmosClient({ endpoint, key });

// Or with connection string
// const client = new CosmosClient(process.env.COSMOS_CONNECTION_STRING!);

export const database: Database = client.database(databaseId);

export function getContainer(containerId: string): Container {
  return database.container(containerId);
}
```

### Type Definitions
```typescript
// types/cosmos.ts
export interface BaseItem {

From alinaqi/maggy, MIT.

More from alinaqi/maggy