Power BI 778 Performance Optimization and Troubleshooting 3

Question 1

What is the dataset size limit per dataset in a Power BI Pro workspace when using Import mode?

Accepted Answer

1 GB

Answer

Power BI Pro workspaces enforce a 1 GB per-dataset limit for Import mode; Premium workspaces support much larger datasets (up to 400 GB with enhanced metadata settings enabled).

Question 2

When writing DAX, which filtering approach is generally more performant for a simple equality condition on a single column?

Accepted Answer

CALCULATE([Measure], Table[Column] = Value)

Answer

Using CALCULATE with a simple filter argument allows the VertiPaq storage engine to apply the filter efficiently, whereas FILTER iterates row by row through the table.

Question 3

How does refactoring a denormalized flat table into a star schema reduce Power BI memory usage?

Accepted Answer

It replaces repeated text strings in the fact table with compact integer keys, improving compression

Answer

Integer foreign keys in a fact table compress far better than repeated text values; the VertiPaq engine achieves much higher compression on integer columns with low cardinality.

Question 4

In Power BI Premium, which feature enables Import mode for historical data partitions while using DirectQuery for the most recent real-time partition of the same table?

Accepted Answer

Incremental refresh with hybrid tables

Answer

Hybrid tables extend incremental refresh so that historical partitions are stored in Import mode for speed, while the latest partition uses DirectQuery to serve real-time data without a full refresh.

Question 5

What DAX practice best reduces repeated evaluation of the same sub-expression within a complex measure?

Accepted Answer

Using VAR to store intermediate results and reference them multiple times

Answer

Declaring a VAR caches the result of an expression so it is evaluated only once; referencing that variable multiple times prevents redundant recalculations by the formula engine.

Power BI 778 Practice Test

Power BI 778 Practice Test

Power BI 778 Performance Optimization and Troubleshooting 3