Question

A retail company has a 400 million row sales fact table stored as Delta tables in a Fabric lakehouse. Analysts complain that the first report interaction each morning is noticeably slow, but subsequent queries are fast. The semantic model uses Direct Lake storage mode. Investigation shows no fallback to DirectQuery is occurring, and the model stays well within capacity guardrails. What is the MOST likely cause of the slow first query?

Accepted Answer

The required column segments must be transcoded and paged into memory from OneLake on the first access (cold cache), after which they remain resident for fast subsequent queries.

Answer

Direct Lake silently falls back to DirectQuery only for the first query of the day and then reverts to VertiPaq.

Answer

The Delta table needs to be re-framed on every first access, which fully reloads all 400 million rows into memory.

Answer

Incremental refresh policies process the historical partitions during the first user query, blocking the report.