AZ-900 Describe Azure architecture and services Practice Question
Which Azure service provides a fully managed time-series database optimized for IoT and operational data?
⚠ Common exam trap
Many exam-takers confuse Azure Data Explorer with Azure Cosmos DB because both can handle time-series data, but Cosmos DB lacks the native time-series optimizations and KQL query language that make ADX the correct answer for fully managed time-series IoT workloads.
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 Data Explorer
Azure Data Explorer (ADX) is a fully managed, high-performance big data analytics service optimized for time-series and log data, making it ideal for IoT and operational scenarios. It uses a columnar storage engine and Kusto Query Language (KQL) to ingest and query massive volumes of time-stamped data with sub-second latency. This directly matches the requirement for a fully managed time-series database for IoT and operational data.
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 it's wrong here
Azure Cosmos DB is a globally distributed, multi-model NoSQL database offering document, graph, key-value, and columnar APIs with millisecond latency and time-to-live expiration. However, ingesting high-velocity time-series data incurs high request-unit (RU) costs, and the platform lacks purpose-built time-series analytics functions like time-bucket aggregation and downsampling. Its strengths are horizontal scaling and low-latency reads, not analytical telemetry pattern detection, so it is not the optimal answer.
- ✓
Azure Data Explorer
Why this is correct
Azure Data Explorer (ADX) is a fast, fully managed data analytics service purpose-built for high-velocity telemetry, logs, and time-series data. It uses columnar storage, automatic partitioning, and the Kusto Query Language (KQL), which includes native time-series operators like bin(), summarize, and series_decompose for pattern analysis. ADX can ingest from Event Hubs and IoT Hub with low latency while applying data compression, making it the correct choice for time-series IoT workloads.
- ✗
Azure SQL Database
Why it's wrong here
Azure SQL Database is a fully managed relational database engine optimized for OLTP transactions with ACID guarantees and row-based storage. Time-series IoT telemetry generates massive, append-only write streams that require columnar compression and high-velocity ingestion, but SQL Database's indexing overhead and locking can throttle throughput. It also lacks native time-series functions such as binning and interpolation, making it a poor fit despite being able to store the data.
- ✗
Azure Table Storage
Why it's wrong here
Azure Table Storage is a NoSQL key-value store that supports schema-less entities and scalable, structured storage for large volumes of data. It does not provide time-series-specific optimizations such as time-based partition keys, append-only ingestion, or built-in aggregation and interpolation functions. While you can store IoT data with a timestamp as a partition key, querying and analyzing high-velocity streams would require custom logic and result in poor performance, making it unsuitable compared to dedicated analytics services.
Go deeper
Related to this question
About these practice questions
Courseiva writes every AZ-900 question from scratch — 981 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-900 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-900 exam.