Extremely Slow Refresh in PowerBI Desktop - Dataflow sources

Query Folding: Ensure that your queries support query folding. Query folding means that Power Query can translate transformations into source queries, reducing the amount of data processed locally. This can significantly speed up data refreshes. Use tools like step folding indicators in Power Query Online to verify .
Incremental Refresh: Implement incremental refresh in your dataflows. This approach refreshes only the data that has changed rather than the entire dataset, reducing refresh time. This method is particularly useful for large datasets.
Dataflow Optimization: Optimize your dataflows by separating the ETL (Extract, Transform, Load) process into different stages. Use staging dataflows to handle initial data extraction and transformation dataflows for subsequent transformations. This separation can improve performance by allowing parallel processing and better resource management.
Enhanced Compute Engine: If you are using Power BI Premium, ensure that the enhanced compute engine is enabled. This engine accelerates query processing and refresh operations by leveraging SQL Cache, which can significantly speed up performance.
Performance Best Practices: Follow best practices for developing dataflows, such as using linked and computed entities to reuse data and reduce redundancy, and performing complex transformations only when necessary. Avoid excessive use of expansive operations like joins and merges on large datasets.
Capacity Management: If you're experiencing slow refresh times due to resource constraints, consider scaling up your Power BI Premium capacity. Adjust the size of your capacity and manage refresh schedules to avoid peak times, which can help distribute the computational load more evenly.
Network Latency: Minimize network latency by ensuring your data sources, dataflows, and Power BI services are located in the same region. This can reduce the time required for data to travel between different components of your infrastructure.

By implementing these strategies, you can optimize your Power BI Desktop refresh times and improve overall performance. If the problem persists, you might also consider reaching out to Power BI support for further assistance.