L10. Core Databases: Azure SQL, Cosmos DB, and Azure Database Services
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Azure offers managed relational and NoSQL databases. The AZ-900 exam tests when to use Azure SQL Database, Azure Cosmos DB, Azure Database for PostgreSQL/MySQL, and Azure Cache for Redis.
Azure SQL Database (PaaS)
Azure SQL Database is a fully managed relational database as a service based on the SQL Server engine. Azure handles patching, backups, high availability, and scaling. Key features:
- Built-in high availability with 99.99% SLA
- Automatic backups with point-in-time restore
- Built-in intelligence for performance tuning
- Supports serverless compute tier (auto-scales to zero when idle)
Azure Cosmos DB
Cosmos DB is a globally distributed, multi-model NoSQL database with single-digit millisecond latency at any scale. Key features:
- Supports multiple APIs: NoSQL (document), MongoDB, Cassandra, Gremlin (graph), Table
- Global distribution: replicate data to any Azure region with automatic failover
- Five consistency levels from Strong to Eventual
- Guaranteed 99.999% availability SLA for multi-region reads
Azure Database for MySQL and PostgreSQL
Fully managed open-source relational databases. Azure handles patching, backups, and high availability. Use when: You have existing MySQL or PostgreSQL workloads you want to move to managed cloud services.
Azure SQL Managed Instance
A nearly 100% compatible SQL Server instance hosted as a PaaS service. Good for migrating on-premises SQL Server instances that use SQL Server-specific features not available in Azure SQL Database.
Azure Cache for Redis
In-memory caching service based on Redis. Dramatically reduces database load by caching frequently accessed data in memory. Use when: Application performance is bottlenecked by database read latency.
Azure SQL vs. Cosmos DB
| Feature | Azure SQL Database | Cosmos DB |
|---|---|---|
| Data model | Relational (tables, rows) | Multi-model: document, key-value, graph |
| Query language | T-SQL | SQL for NoSQL, MongoDB API, etc. |
| Scale | Vertical + read replicas | Horizontal, limitless |
| Global | Multi-region with read replicas | Native global distribution |
| Best for | OLTP, structured data | Real-time, globally distributed |
- ✓Azure SQL Database is a managed relational database based on SQL Server; Azure manages patching, backups, and HA
- ✓Cosmos DB is a globally distributed multi-model NoSQL database with single-digit millisecond latency
- ✓Cosmos DB supports multiple APIs: NoSQL (document), MongoDB, Cassandra, Gremlin, and Table
- ✓Azure SQL Managed Instance provides near-100% SQL Server compatibility for complex migration scenarios
- ✓Azure Cache for Redis is an in-memory caching layer that reduces database read latency
1. A retail application needs to store user shopping cart data with sub-10ms read latency for customers worldwide. Which database service is most appropriate?
2. Which Azure database service is best suited for migrating an existing SQL Server on-premises database with minimal changes?
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This free course covers the theory. Pluralsight adds guided video paths, hands-on Azure labs, and timed practice exams to help you pass AZ-900 with confidence.