Well-designed Power BI reports have the potential to load quickly if they are devoid of complicated data models and sophisticated calculations. But when drastic measures need to be taken to improve performance, the following model and calculation-related actions should be taken.
Optimize the Data Model: Assess the necessity of each of the components of your data model and eliminate the unneeded tables, columns, or relationships. Also, the level of detail in the data should be reduced so that Power BI works on less data. Another option is to use a flattened data model, as the only joins that would be required are between the fact table and associated dimensions, and no complex joins would be needed. As star schema designs generally work fine in Power BI, opt for this table arrangement for better results.
Refine DAX Calculations: In implementing more sophisticated computations, the use of calculated columns should be minimized where possible since they contribute to the expansion of model size. Use measures instead, which perform calculations only when required. Dismiss unnecessary calculations from your DAX expressions, implement variables to interim results, and make certain the functions employed in DAX are at par with data volumes. Use these instead of the heavy-weight ones because there are usually fewer complex functions that achieve the same logic. Avoid using complex time intelligence calculations where simpler time intelligence calculations can suffice.
Optimize Data Refresh and Queries:
- To lessen the burden on the model, use Power Query to perform transformations at the source level rather than in Power BI.
- Do not bring in irrelevant data—do this as early as possible. Only bring in what is required into the model. Do not bring in large volumes of data that will not be currently used.
- Try to provide incremental refresh as well to the very large datasets that you are working with. This will enable the update of only new or modified data, thus lessening the time and costs spent on format updates.
With these aspects addressed, one can expect significant improvement in load times and the overall usability of Power BI reports.