Power BI 778 Performance Optimization and Troubleshooting 1 — Questions and Answers
Question 1: Which Power BI storage mode loads all data into the in-memory VertiPaq engine for the fastest query performance?
- DirectQuery
- Import (Correct answer)
- Live Connection
- Composite
Correct 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.
Question 2: Which built-in Power BI Desktop tool records and displays the rendering time for each visual on a report page?
- Query Diagnostics
- Performance Analyzer (Correct answer)
- DAX Studio
- Data Profiler
Correct 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.
Question 3: What Power BI feature partitions historical data and refreshes only the most recent portion, reducing refresh duration for large datasets?
- Scheduled refresh
- Dataflows
- Incremental refresh (Correct answer)
- Composite model
Correct 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.
Question 4: What is 'query folding' in Power Query?
- Combining multiple queries into a single query step
- Pushing transformation steps back to the data source to execute natively (Correct answer)
- Folding a Power Query expression into a DAX measure
- Merging results from two different data sources
Correct 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.
Question 5: What is a common performance drawback of excessive bidirectional cross-filtering in a Power BI data model?
- It reduces the number of available DAX functions
- It can create ambiguous filter paths, leading to slower queries and unexpected results (Correct answer)
- It prevents the use of calculated columns
- It forces all tables into DirectQuery mode
Correct 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.
Question 6: Which column characteristic allows the VertiPaq engine to achieve the highest compression ratio?
- High-cardinality text columns
- Low-cardinality integer columns (Correct answer)
- DateTime columns with millisecond precision
- Decimal columns with many unique values
Correct 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.
Question 7: Which Power BI storage mode allows some tables to use Import while others use DirectQuery within the same dataset?
- Dual mode
- Live Connection
- Composite model (Correct answer)
- Push dataset
Correct 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.
Power BI 778 Performance Optimization and Troubleshooting 1
Which Power BI storage mode loads all data into the in-memory VertiPaq engine for the fastest query performance?