Question

You are building a Direct Lake semantic model on an F64 capacity over a lakehouse fact table that contains 4.2 billion rows. During validation you observe that queries against this table consistently fall back to DirectQuery, and performance is worse than expected. You confirm the SQL analytics endpoint is healthy and there is no memory eviction occurring. What is the most likely cause of the DirectQuery fallback?

Accepted Answer

The fact table exceeds the maximum row count per table guardrail for Direct Lake on the current capacity SKU, forcing DirectQuery.

Answer

Direct Lake does not support fact tables larger than 1 billion rows under any circumstance and must always use Import mode instead.

Answer

The lakehouse Delta table is missing a primary key, which Direct Lake requires to load columns into VertiPaq.

Answer

Direct Lake automatically reverts to DirectQuery whenever a table participates in a relationship, regardless of size.