AZ-900 Describe Azure architecture and services Practice Question
Which Azure service provides NoSQL wide-column database storage compatible with Apache Cassandra?
⚠ Common exam trap
Test-takers frequently confuse Azure Table Storage (a key-value store) with a wide-column database, or assume that any NoSQL service (like Redis) can substitute for Cassandra's specific data model and protocol compatibility.
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 for Apache Cassandra
Azure Cosmos DB for Apache Cassandra is the correct choice because it provides a NoSQL wide-column database storage that is fully compatible with the Apache Cassandra Query Language (CQL) and wire protocol. This allows you to run existing Cassandra workloads and tools (like cqlsh and Cassandra drivers) directly on Azure without any code changes, while benefiting from Cosmos DB's global distribution and SLA-backed performance.
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 Table Storage
Why it's wrong here
Azure Table Storage is a NoSQL key-value store that uses a flat namespace of tables and partitions, accessed via OData endpoints or SDKs, but it does not implement the Cassandra wire protocol or support Cassandra Query Language (CQL). Its data model is a simple collection of entities with named properties, not a wide-column store with clustering keys, materialized views, or Cassandra-specific features like lightweight transactions. Therefore, while it is a cloud NoSQL offering, it cannot serve as a drop-in replacement for Cassandra-based applications.
- ✓
Azure Cosmos DB for Apache Cassandra
Why this is correct
Azure Cosmos DB for Apache Cassandra is a fully managed database service that natively supports the Cassandra wire protocol and CQL, allowing existing Cassandra drivers, tools, and applications to connect without code changes. It provides a wide-column NoSQL model that matches Cassandra's partition-key and clustering-key semantics, while adding Azure-specific benefits such as global distribution, multiple consistency levels, 99.999% availability SLAs, and serverless or provisioned throughput models. This makes it the correct choice for teams seeking Cassandra compatibility with reduced operational overhead.
- ✗
Azure Cache for Redis
Why it's wrong here
Azure Cache for Redis is an in-memory data store that implements the Redis protocol, offering data structures like strings, hashes, lists, and sorted sets, and is primarily used as a low-latency cache or session store. It lacks persistence guarantees expected of a durable database by default, and it does not support Cassandra's CQL or wide-column data model. Since it is not designed for long-term storage, high-volume analytical queries, or replicating Cassandra's partitioning and replication behavior, it cannot fulfill Cassandra compatibility requirements.
- ✗
Azure SQL Database Hyperscale
Why it's wrong here
Azure SQL Database Hyperscale is a relational database service based on the SQL Server engine, using T-SQL for queries, schemas with fixed columns, and ACID transactions. It is not a NoSQL or wide-column store, and it does not expose any Cassandra-compatible interfaces such as CQL or the Cassandra wire protocol. Hyperscale's architecture focuses on dynamically scaling compute and storage for high-throughput OLTP and reporting workloads, which is fundamentally different from a Cassandra-style distributed database designed for massive write-heavy workloads with eventual consistency.
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Azure Regions and Geographies
Key term
SLA
A Service Level Agreement (SLA) is a contract between a service provider and a customer that defines the level of service expected, including metrics like uptime, response time, and penalties for non-compliance.
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.
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