Debugging the DAX and Power Query can be quite tricky while working on Power BI due to the different transformations and calculations involved. Fortunately, here are some helpful tools and techniques that can help in identifying and rectifying the problem in a faster manner:
DAX Studio: DAX Studio is arguably the most powerful tool for troubleshooting DAX. Compared to using Power BI alone, DAX Studio offers a more complete environment for examining and improving your DAX calculations. Additionally, you will be able to assess the performance of each query in your DAX and analyze the time taken to perform each section and the resources each section of the DAX uses. This is useful in identifying the weak areas of your calculations for enhancement. In this way, DAX Studio helps to understand the cause of incorrect or unexpected behavior by offering measures that are separated from other codes.
Performance Analyzer: Power BI has a built-in analyzer that helps evaluate the performance of the reports, and this helps to identify any bottlenecks in the embedded report views. When you perform Performance Analyzer, you will see the breakdown of execution time per each visual and what is the report rendering bottleneck. This is very useful in case the problem is due to bad DAX calculations. You can also transfer the logs to DAX Studio for further exploration, where you can go into detail concerning the offending measures or visuals and do what is required.
An Insightful Look at Power Query Diagnostics: Power Query is equipped with a diagnostic feature that analysts rely on to investigate issues with query performance. Once the "Diagnostics" option is turned on within the Power Query Editor, logs of every single query step can be captured in detail, indicating the delays or refresh error-causing steps in the processes. This tool also provides data on how resources are being used at each step, allowing you to pinpoint the transformations or data loads that are excessive and causing the problem. Finally, a useful strategy is to test each query step and see which one is responsible for the error.
Highlighting Errors and Solution Building: Solution Build includes Error Highlighting and Stepwise Debugging in Power Query. Power Query is linear: at each transformation step, the results of the transformation are shown at the intermediate step. When there is an error while acting Power Query, that action is usually highlighted in red, making it easy to determine where to focus one's corrective efforts. This is because adding new transformations will warrant a thorough examination of all the steps, which is a very impromptu way of debugging. Or, if needed, you can try to remove some steps and check if such a change helps to process the query without these steps.
Employing Variables in DAX: The use of variables (VAR) can enhance the debugging process of complex DAX calculations. It is easier to follow each of the named steps for a particular calculation of the formula instead of trying to grasp the entirety of the formula at a go. This 'bloating' of complex letters into weak focus modules not only favors the readability of the clause but also enables the user to verify the correctness of the separate components of the calculation before joining them for the last measure.
AI Applications, Bots, and Copilot: One such application, Microsoft's Power BI Copilot, if it exists in the version available, helps in the identification of certain problems and proposes corrective measures or recommends optimization techniques. It is common for the Users of Copilot to onboard the tool while creating or perfecting DAX queries using the tool, thus making it less prone to use and increasing faster performance. Other tools, such as ChatGPT, may as well explain the elements of complicated DAX functions or Power Query operations, including discussing the common mistakes that users make and what they need to do best.
The combination of these tools and methods greatly enhances the debugging capabilities in Power BI, as it allows for error containment and code optimization without fear.
