Performance Optimization and Troubleshooting Flashcards

Which Power BI storage mode loads all data into the in-memory VertiPaq engine for the fastest query performance?

Answer: Import

Import mode physically copies data into Power BI's in-memory VertiPaq engine, enabling the fastest query performance since no source queries are needed at report time.

Which built-in Power BI Desktop tool records and displays the rendering time for each visual on a report page?

Answer: Performance Analyzer

Performance Analyzer, found in the View ribbon, records the time each visual takes to render, including DAX query time, DirectQuery time, and other overhead.

What Power BI feature partitions historical data and refreshes only the most recent portion, reducing refresh duration for large datasets?

Answer: Incremental refresh

Incremental refresh partitions data by a date/time column and only refreshes recent partitions, dramatically cutting refresh time for large historical datasets.

What is 'query folding' in Power Query?

Answer: Pushing transformation steps back to the data source to execute natively

Query folding occurs when Power Query translates your transformation steps into a native source query (such as SQL), allowing the source system to perform the work rather than Power BI.

What is a common performance drawback of excessive bidirectional cross-filtering in a Power BI data model?

Answer: It can create ambiguous filter paths, leading to slower queries and unexpected results

Bidirectional cross-filtering multiplies the filter propagation paths the engine must evaluate, causing ambiguity and performance degradation in complex models.

Which column characteristic allows the VertiPaq engine to achieve the highest compression ratio?

Answer: Low-cardinality integer columns

VertiPaq compresses columns based on cardinality; integer columns with few distinct values achieve the highest compression because the engine stores only a small dictionary plus a compressed index.

Which Power BI storage mode allows some tables to use Import while others use DirectQuery within the same dataset?

Answer: Composite model

Composite models allow mixing Import and DirectQuery storage modes within a single dataset, letting you optimize each table's mode based on size and refresh requirements.