What is DirectQuery, and how does it differ from Import mode?

DirectQuery:

1. Data Connection: In DirectQuery mode, data remains in the source system (e.g., a database server), and Power BI queries the data in real-time when you interact with reports and visuals. This means you're working with live data, and any changes in the source are reflected immediately in your reports.

2. Data Volume: DirectQuery is ideal for scenarios where you have a large amount of data that cannot be loaded into memory due to resource constraints. You don't need to worry about data storage limitations in Power BI.

3. Data Transformations: Unlike Import mode, data transformations and modeling are primarily performed in the source system, making DirectQuery less flexible in terms of data shaping and modeling within Power BI.

4. Complex Queries: DirectQuery supports complex queries, including those that involve multiple data sources and complex joins.

5. Performance: The performance of DirectQuery depends on the responsiveness of the source system and the efficiency of the queries. It may not be as fast as Import mode for certain operations.

Import Mode:

1. Data Loading: In Import mode, data is loaded from the source into Power BI's internal data model. Once loaded, it resides in-memory, enabling fast and interactive data analysis. The data is a snapshot at the time of import.

2. Data Volume: Import mode is suitable for smaller to medium-sized datasets that can fit in memory. It's an excellent choice for optimizing performance, as data retrieval is significantly faster from memory compared to querying a source system.

3. Data Transformations: In Import mode, you have extensive flexibility to transform and model the data within Power BI using the Power Query Editor. This allows you to create calculated columns, measures, and custom calculations, providing a more powerful and versatile data modeling experience.

4. Data Refresh: You need to periodically refresh the data in Import mode to keep it up-to-date. This means that any changes in the source data will only be reflected in your reports after a refresh operation.

5. Performance: Import mode generally provides superior performance for report rendering, interactive exploration, and responsiveness, as the data is already in-memory.

In summary, the choice between DirectQuery and Import mode in Power BI depends on your specific data requirements and performance considerations. DirectQuery is suitable for large datasets and scenarios where real-time data access is crucial. Import mode is ideal for smaller datasets and situations where performance and data modeling flexibility are a priority.

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