Mix Data Modes Without Slowing Down Power BI.

• Mix Data Modes Without Slowing Down Power BI

What Are They?

• A Composite Model blends Import and DirectQuery modes.
• It allows a single report to use both types.
• Import mode caches data in Power BI for speed.
• DirectQuery mode runs queries live on the source database.
• Use it when you need real-time data on top of historical data.
• It is powerful but requires careful planning.

The Golden Rule

• Push transformations to the source system whenever possible.
• Avoid complex calculated columns in DirectQuery tables.
• Let the database engine do the heavy lifting.
• Use Import mode for small, frequently filtered tables.
• Use DirectQuery for large, frequently updated tables.
• Prioritize performance over minor data preparation convenience.

Optimize Storage Modes

• Set smaller tables to Dual or Import mode.
• These can act as filters for larger DirectQuery tables.
• This reduces the number of queries sent to the source.
• Use Import for static data like date or category tables.
• Use DirectQuery for fact tables with billions of rows.
• Review table properties to assign the correct storage mode.

Mind Your Relationships

• Ensure relationships are based on indexed database columns.
• Prefer single-directional relationships in the model.
• Avoid bi-directional relationships across Composite Models.
• They can force unnecessary data source queries.
• Use integer-based keys for relationships for best performance.
• Validate relationships to prevent cross-database joins if possible.

Calculated Columns Caution

• Creating calculated columns on DirectQuery tables is expensive.
• Each is computed during the query, slowing response time.
• Create these columns in the source database instead.
• If you must, keep them very simple.
• Use Import mode for tables requiring complex calculations.
• This improves overall report rendering speed.

Limit Visual Interactions

• Each visual can trigger a query to the database.
• Too many interactive visuals on one page creates congestion.
• Use bookmarks and buttons to navigate instead.
• Design pages with a clear purpose and limited visuals.
• Use slicers wisely, as they trigger queries on change.
• Test page performance with all interactions enabled.

Leverage Aggregations

• Use Aggregations to dramatically improve performance.
• Create an Import summary table for a huge DirectQuery fact table.
• Power BI automatically uses the faster Import aggregate.
• It only goes to DirectQuery for detailed drill-through.
• This is a top technique for managing massive datasets.
• It provides a balance between speed and data freshness.

Test and Monitor

• Always test with realistic data volumes and user filters.
• Use Performance Analyzer in Power BI Desktop to find bottlenecks.
• Monitor query execution times on your database server.
• Start simple and add complexity only if needed.
• Document your model's design for future reference.
• A well-planned model is a fast and scalable model.