Improve DirectQuery Performance Without Changing the Data Source: Use Aggregations

Quick Answer

Aggregations are the answer because they let Power BI intercept and answer many report queries using a small, pre-summarized table instead of sending every request straight through to the SQL Server data warehouse, which is exactly the kind of performance gain this scenario needs without touching the source itself. A DirectQuery report normally sends a live query to the source every time a visual needs data, so when the source is large or the network round-trip is slow, users feel it directly as report lag. By building an aggregated table at a higher granularity and letting it serve as a stand-in for the detailed DirectQuery table whenever a query can be satisfied at that summary level, Power BI only falls back to the full DirectQuery request for the rare cases that need row-level detail. This keeps the underlying data source and connection mode completely unchanged, which matters here since the requirement is explicitly to improve performance without modifying the source. The general principle to take away is that DirectQuery performance problems are often solved inside Power BI itself, through techniques like aggregations that reduce how often and how much data has to be pulled live from the source, rather than by upgrading the source or switching the whole model to Import mode.