For an Azure Fabric based data platform we are building I'm evaluating PowerBI as a possible reporting solution. My knowledge of PowerBI is almost non existant so there are a lot of things I learned along the way.
My first lesson learned:
There are multiple ways to fetch data in PowerBI.
I learned this lesson quite fast when I tried to connect to my first datasource. After selecting the ‘Import data from database’ option I immediately got to choose a Data Connectivity mode:
The available options were:
- Import
- DirectQuery
Let’s find out what each of these options mean and what exactly is the difference.
Import mode
This mode should be your first choice. As the name implies in this mode the data is imported in the report. When querying the data everything is loaded into memory which gives really fast query performance.
This sounds a good idea for really small datasets but what if you have a lot of data? PowerBI makes it possible to work with big datasets by compressing the data (a 10-times compression is not unusable). Storing it on disk makes it even more smaller.
This makes the import mode a good default for most datasets.
Remark: Be aware that the data is only as current as the latest refresh.
DirectQuery mode
A second mode is DirectQuery. When you use DirectQuery, the Power BI report does not store the data locally, which can be advantageous for scenarios where you want to ensure that the report always reflects the most up-to-date data from the source system. This is especially useful when dealing with large datasets that may be impractical to import into Power BI.
However, it's important to note that DirectQuery has some limitations and considerations. Not all data sources support DirectQuery, and the performance of your reports may depend on the speed and capabilities of your underlying data source. Additionally, some Power BI features may not be available or may behave differently when using DirectQuery compared to importing data.
Remark: There is also a third Composite mode that allows to mix Import and DirectQuery modes, or integrate multiple DirectQuery data sources.
More information
Dataset modes in the Power BI service - Power BI | Microsoft Learn