AZ-305 Design data storage solutions Practice Question
A global e-commerce company needs a database solution that can handle high-velocity writes from user transactions across multiple regions. They require multi-region writes with automatic conflict resolution and single-digit millisecond latency for reads and writes. Which Azure data store should they use?
⚠ Common exam trap
Candidates often confuse Azure SQL Database's active geo-replication (which supports only read-scale secondaries) with true multi-region writes, or they assume Azure Table Storage's global replication is equivalent to Cosmos DB's active-active capability.
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 the correct choice because it offers multi-region writes with automatic conflict resolution using last-writer-wins (LWW) or custom conflict resolution policies, and it guarantees single-digit millisecond latency for both reads and writes at the 99th percentile. Its globally distributed, multi-model design is purpose-built for high-velocity transactional workloads that require active-active replication across 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 Cosmos DB
Why this is correct
Correct. Azure Cosmos DB is a globally distributed, multi-model database service that natively supports multi-region writes (multi-master) with automatic conflict resolution via last-writer-wins or custom conflict resolution policies, ensuring active-active failover across regions. Its turnkey global distribution replicates data to any number of Azure regions, providing single-digit millisecond read and write latency at the 99th percentile, and it exposes multiple consistency models (strong, bounded staleness, session, consistent prefix, eventual) to balance consistency and performance. This makes it the only listed option that directly satisfies the requirement for a database that can handle global writes with automatic conflict resolution.
- ✗
Azure Table Storage
Why it's wrong here
Wrong. Azure Table Storage is a scalable NoSQL key-value store that supports geo-redundant storage (GRS) for read-access geo-redundant storage (RA-GRS), but this only provides read access to a secondary region after a failover; writes are always directed to a single primary region. The service does not support multi-region writes or automatic conflict resolution—there is no active-active capability, so a globally distributed e-commerce application requiring writes from multiple regions would experience a single point of failure for write availability and would need application-level conflict handling, which is not provided.
- ✗
Azure SQL Database
Why it's wrong here
Wrong. Azure SQL Database offers active geo-replication and failover groups, but these are designed for a single primary write region; readable secondaries in other regions are read-only, and writes must go to the primary. While failover groups allow the secondary to become the new primary during a regional outage, this is a failover operation, not simultaneous multi-region writes, and there is no built-in conflict resolution for concurrent writes to different regions. Thus, it does not meet the requirement for automatic multi-writer support.
- ✗
Azure Redis Cache
Why it's wrong here
Wrong. Azure Redis Cache is an in-memory data store, not a durable database designed for transactional persistence and multi-region write consistency. It does support geo-replication for cache instances, but the replication is asynchronous and unidirectional from the primary to the read replica(s); writes are not accepted on the replica, and there is no conflict resolution because there are no independent multi-writer regions. It is intended for caching and low-latency data access, not as the authoritative database for a global e-commerce transaction system where durable, conflict-free writes are essential.
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