Question

You publish a Direct Lake semantic model over a large Delta table in a Fabric lakehouse. During peak usage, users report that some visuals become noticeably slower and analysts observe that certain queries no longer benefit from in-memory VertiPaq column loading. In Performance Analyzer you notice these queries are being executed as DirectQuery against the SQL analytics endpoint. The model's DirectLakeBehavior property is left at its default value. What is the MOST likely cause of this behavior?

Accepted Answer

The Delta table exceeded a Direct Lake guardrail (such as the maximum rows per table or the row group / memory limit for the capacity SKU), triggering automatic fallback to DirectQuery.

Answer

Incremental refresh policies were applied to the model, which forces all queries to run in DirectQuery mode.

Answer

The semantic model was configured in Import storage mode, so queries are cached and periodically re-executed against the source.

Answer

Object-level security was enabled on the fact table, which disables VertiPaq column encoding and forces DirectQuery.