azure-cosmosdb

## 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", "de...