Which Azure database service stores time-series data from IoT devices for long-term trend analysis and anomaly detection?
Azure Data Explorer (ADX) is optimized for real-time analytics on time-series data from IoT and telemetry sources.
Why this answer
Azure Data Explorer (ADX) is a fully managed, high-performance big data analytics service optimized for interactive analysis of large volumes of time-series and log data. It uses the Kusto Query Language (KQL) to ingest, index, and query streaming telemetry from IoT devices, enabling long-term trend analysis and anomaly detection through built-in time-series functions like `series_decompose()` and `series_fit_line()`.
Exam trap
The trap here is that candidates often confuse Azure Cosmos DB's support for IoT device state storage with the need for a dedicated time-series analytics engine, overlooking that Cosmos DB lacks native time-series decomposition and anomaly detection functions required for long-term trend analysis.
How to eliminate wrong answers
Option A is wrong because Azure Cosmos DB is a multi-model NoSQL database designed for globally distributed, low-latency transactional workloads (e.g., real-time app data), not for high-throughput time-series analytics or long-term trend analysis. Option C is wrong because Azure Table Storage is a key-value NoSQL store for semi-structured data with limited query capabilities and no native time-series functions, making it unsuitable for complex anomaly detection over large historical datasets. Option D is wrong because Azure SQL Database is a relational database optimized for OLTP (online transaction processing) with row-based storage, not for the columnar, append-only, high-ingestion-rate workloads typical of IoT time-series data.