What is a common use case for Kinesis Data Analytics?

Kinesis Data Analytics is specifically designed to process and analyze streaming data in real time. It allows users to run SQL queries on the streaming data and perform transformations that can be integrated into data pipelines. A common use case is transforming data for real-time ETL (Extract, Transform, Load) processes, where immediate insights or actions are needed based on the stream of incoming data.

This service can handle various types of streaming data and apply analytics that help in deriving immediate information from the incoming stream. Through this capability, organizations can react quickly to changes in the data, enabling them to make informed decisions rapidly without having to wait for batch processing that could delay insights.

While the other options might relate to data handling and processing in AWS, they don't specifically pertain to the primary functionalities of Kinesis Data Analytics. For instance, the ingestion from legacy databases is typically performed using AWS Database Migration Service or Kinesis Data Firehose, not directly by Kinesis Data Analytics. Messaging queues for asynchronous processing are more aligned with services like Amazon SQS, and storing large volumes of unstructured data is better suited for AWS S3 or Amazon DynamoDB. Thus, the focus on real-time ETL transformation distinctly outlines the primary use case for Kinesis Data Analytics.