AZ-500 · Question #635
AZ-500 Question #635: Real Exam Question with Answer & Explanation
Azure PostgreSQL Hotspot Question — Explained The key requirements are: row-based sharding for horizontal write scaling + minimal administrative effort (managed service). --- Dropdown 1: Azure Service Correct: Azure Cosmos DB for PostgreSQL This service (formerly "Azure Databas
Question
Hotspot Question You have an Azure subscription. You plan to deploy a high-throughput transactional workload that will use PostgreSQL. You need to recommend a managed solution for storing relational data. The solution must meet the following requirements: - Support the horizontal scaling of transactional writes by using row- based sharding. - Minimize administrative effort. What should you include in the recommendation? To answer, select the appropriate options in the answer area. NOTE: Each correct selection is worth one point. Answer:
Options
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Explanation
Azure PostgreSQL Hotspot Question — Explained
The key requirements are: row-based sharding for horizontal write scaling + minimal administrative effort (managed service).
Dropdown 1: Azure Service
Correct: Azure Cosmos DB for PostgreSQL
This service (formerly "Azure Database for PostgreSQL – Hyperscale (Citus)") is built on the open-source Citus extension, which adds a distributed coordinator/worker node architecture on top of standard PostgreSQL. It is the only option that natively supports horizontal sharding of transactional writes across multiple nodes using a distribution column. It is fully managed by Microsoft, satisfying the minimal-admin requirement.
| Option | Why Wrong |
|---|---|
| Flexible Server | Single-node managed PostgreSQL. Supports vertical scaling and read replicas, but has no native horizontal write sharding. |
| Single Server | Legacy, deprecated single-node offering. No sharding capability whatsoever. |
Dropdown 2: Scalability Technique
Correct: Distributed tables
In Citus/Cosmos DB for PostgreSQL, distributed tables are tables whose rows are partitioned across worker nodes using a distribution column (hash-based or range-based). Each shard holds a subset of rows — this is precisely row-based sharding. Writes are routed to the correct shard automatically by the coordinator, enabling true horizontal write scaling.
| Option | Why Wrong |
|---|---|
| Logical replication | A PostgreSQL feature for streaming changes between databases/instances. It replicates data — it does not partition or shard writes horizontally. |
| Near-zero downtime scaling | Refers to live vertical scaling (resize compute/storage with minimal disruption). Has nothing to do with distributing writes across shards. |
Core Concept Summary
Row-based sharding = rows of a table are distributed across multiple physical nodes based on a distribution key. Only Azure Cosmos DB for PostgreSQL (via Citus) implements this natively as a managed Azure service, and the mechanism is called distributed tables.
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