In the described dataflow with two lakehouses, non-folded steps are executed by which engine?

• A. Each lakehouse's query engine
• B. The Microsoft Power Query engine
• C. The source lakehouse query engine
• D. The VertiPaq engine

Answer: (B)

Non-folded steps are transformations that can’t be translated into the lakehouse’s native query language and therefore can’t be pushed down to the data source. In a dataflow with two lakehouses, these steps must be executed by the Microsoft Power Query engine, which runs the M-based transformations as data moves through the flow. This engine handles the remaining work after pulling data from the sources, ensuring the requested operations are completed even when the source engines can’t fold them.

The lakehouse query engines would perform folding for steps that they can translate into their native queries, and the VertiPaq engine is the in-memory execution engine used for Power BI data models—not the place where non-folded transformations in a dataflow are executed.