AZ-900 Describe Azure architecture and services Practice Question
Which Azure service provides a globally distributed, multi-model database service with single-digit millisecond read latency?
⚠ Common exam trap
Many exam-takers confuse Azure Cache for Redis (a low-latency cache) with a globally distributed multi-model database, but Redis is not a multi-model database and does not provide turnkey global distribution with multiple consistency models like Cosmos DB does.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Azure Cosmos DB
Azure Cosmos DB is a globally distributed, multi-model database service that guarantees single-digit millisecond read latency at the 99th percentile, regardless of the region or consistency level. It supports multiple data models (document, key-value, graph, column-family) and provides turnkey global distribution across any number of Azure regions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Azure SQL Database
Why it's wrong here
Azure SQL Database is a managed relational database service based on the SQL Server engine. While it offers built-in high availability and can be configured for geo-replication, it is not a multi-model NoSQL database, nor does it provide turnkey global distribution with single-digit millisecond latency at any scale. Its latency and consistency characteristics are tied to a primary region, requiring manual failover for cross-region scenarios, so it does not match the described planet-scale, multi-region, low-latency requirements.
- ✗
Azure Database for MySQL
Why it's wrong here
Azure Database for MySQL is a managed service for MySQL, a single-model relational database. It does not natively support document, graph, key-value, or columnar data models like Cosmos DB does, and its global distribution is limited to read replicas in paired regions with eventual consistency, not multi-region writes with a 99.999% SLA. This makes it unsuitable for the described globally distributed multi-model NoSQL scenario, as it is fundamentally a different type of database with different scalability and latency guarantees.
- ✓
Azure Cosmos DB
Why this is correct
Azure Cosmos DB is Microsoft's globally distributed, multi-model NoSQL database service. It provides turnkey distribution across any number of Azure regions, with multiple consistency levels and a 99.999% availability SLA for multi-region writes. It supports document, key-value, graph, and columnar APIs, and offers single-digit millisecond read and write latency at the 99th percentile, making it the only option that matches all the described characteristics of a globally distributed, multi-model NoSQL database.
- ✗
Azure Cache for Redis
Why it's wrong here
Azure Cache for Redis is an in-memory caching solution, not a primary database. It stores data in a volatile in-memory cache, optimized for low-latency reads of frequently accessed data, but it does not provide a durable, multi-model data store or global distribution with a 99.999% SLA. Its lack of multi-region write capabilities and reliance on memory means it cannot serve as the globally distributed multi-model database described in the question, making it clearly incorrect for this scenario.
Go deeper
Related to this question
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Azure Regions and Geographies
Key term
Azure Cosmos DB
Azure Cosmos DB is a fully managed, globally distributed NoSQL database service that offers fast reads and writes anywhere in the world with automatic scaling and multiple consistency models.
Key term
Region
A region is a distinct geographic location where a cloud provider operates multiple data centers that are connected by low-latency networks and provide cloud services.
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