PL-300 Visualize and analyze the data Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  Create an index on the Region column in the source database

  Why this is correct

  In DirectQuery mode, Power BI does not store a local copy of the data; every visual and slicer interaction sends a native query (usually SQL) to the source database. Creating an index on the Region column directly reduces the cost of the WHERE clause filter generated by the slicer, allowing the database engine to perform a seek rather than a full table scan. This is the most effective troubleshooting step because it optimizes the actual bottleneck—source-side predicate evaluation—without changing the semantic model or losing data granularity.

• ✗

  Increase the cache size in Power BI Desktop

  Why it's wrong here

  Cache size in Power BI Desktop controls the memory allocated for storing imported data in Import mode, so adjusting it has no effect on DirectQuery connections. DirectQuery bypasses the local cache entirely and executes queries against the remote source on demand; therefore, increasing the cache size in Power BI Desktop will not improve report performance and may even be misleading as a troubleshooting action. Performance in DirectQuery is governed by source database query plans, network latency, and gateway throughput, none of which are addressable by client-side cache settings.

• ✗

  Switch the model to Import mode

  Why it's wrong here

  Although Import mode typically offers faster query response times by maintaining an in-memory compressed snapshot, it is not a general-purpose substitute for DirectQuery because it sacrifices real-time data accuracy and requires scheduled refresh or full loads. In scenarios where the underlying data changes frequently or is subject to Row-Level Security (RLS) at the source, Import mode may be non-compliant or impractical. Switching models is a major architectural change that involves storage, refresh, and data-currency trade-offs; it is not a targeted fix for a DirectQuery-specific performance issue and may be unavailable due to size or governance constraints.

• ✗

  Reduce the number of distinct values in Region

  Why it's wrong here

  Lowering the cardinality of the Region column by consolidating or grouping values is an anti-pattern that can degrade analytical usefulness and does not address the physical query execution cost—the database still has to scan or seek the underlying table based on the predicate. Even with fewer distinct values, the search complexity for a filter remains similar unless the column is indexed; the source database query optimizer may also produce the same access plan if the column selectivity changes only marginally. Moreover, reducing distinct values irreversibly loses business detail (e.g., merging regional territories) and undermines the purpose of having a slicer, making it an unacceptable trade-off for performance.

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