When working with Power BI, one of the most critical decisions you'll make is selecting the appropriate data connectivity mode: DirectQuery or Import. Each approach has distinct characteristics that suit different scenarios.
**Import Mode:**
Import mode loads data into Power BI's in-memory engine,…When working with Power BI, one of the most critical decisions you'll make is selecting the appropriate data connectivity mode: DirectQuery or Import. Each approach has distinct characteristics that suit different scenarios.
**Import Mode:**
Import mode loads data into Power BI's in-memory engine, creating a compressed and optimized copy of your data. This approach offers the fastest query performance since all calculations happen locally within Power BI's VertiPaq engine. You can use the full range of DAX functions and transformations. However, the data represents a snapshot from the last refresh, meaning you need to schedule refreshes to keep information current. Import mode works best when your dataset fits within memory constraints (typically up to 1GB for shared capacity or larger for Premium), when you need complex calculations, or when source systems cannot handle frequent queries.
**DirectQuery Mode:**
DirectQuery maintains a live connection to your data source, sending queries back to the source system whenever users interact with reports. This ensures you always see real-time data, which is essential for scenarios requiring up-to-the-minute accuracy. DirectQuery is ideal when dealing with massive datasets that exceed memory limitations or when data freshness is paramount. However, report performance depends on your source system's speed and capacity. Some DAX functions and modeling features have limitations, and the source database must handle all query loads.
**Key Considerations:**
- Data volume: Large datasets favor DirectQuery
- Freshness requirements: Real-time needs favor DirectQuery
- Performance expectations: Faster visuals favor Import
- Source system capabilities: Robust databases handle DirectQuery better
- Transformation complexity: Advanced calculations favor Import
**Hybrid Approach:**
Power BI also supports composite models, allowing you to combine both modes within a single model, giving you flexibility to optimize based on specific table requirements.
Choosing wisely ensures optimal performance and user satisfaction with your Power BI solutions.
Choose between DirectQuery and Import
Why is This Important?
Understanding when to use DirectQuery versus Import mode is a fundamental decision for every Power BI solution. This choice impacts report performance, data freshness, model capabilities, and infrastructure requirements. The PL-300 exam heavily tests this concept because it demonstrates your ability to design appropriate data solutions based on business requirements.
What is DirectQuery?
DirectQuery is a connection mode where Power BI does not store data locally. Instead, it sends queries to the source database in real-time whenever users interact with reports. The data remains in the original data source, and Power BI acts as a pass-through layer.
What is Import Mode?
Import mode loads and stores data within the Power BI dataset. The data is compressed and optimized using the VertiPaq engine, enabling fast query performance. Data must be refreshed periodically to stay current.
How DirectQuery Works:
1. User interacts with a visual in a report 2. Power BI generates a query in the native language of the data source 3. Query is sent to the source database 4. Database processes the query and returns results 5. Power BI renders the visual with returned data
How Import Mode Works:
1. During refresh, Power BI connects to data sources 2. Data is extracted, transformed, and loaded into the model 3. VertiPaq engine compresses and stores data in memory 4. Queries run against the local cached data 5. Scheduled or manual refresh updates the dataset
When to Choose DirectQuery:
• Data must be current to the second (real-time requirements) • Dataset size exceeds Power BI's 1GB limit (Pro) or storage constraints • Security rules must be enforced at the database level • Source system has existing optimized infrastructure • Regulatory requirements mandate data stays in the source
When to Choose Import:
• Best query performance is required • Complex DAX calculations and measures are needed • Data sources have limited query capacity • Full modeling capabilities are required • Data can tolerate periodic refresh schedules • Multiple data sources need to be combined
Key Limitations of DirectQuery:
• Performance depends on source database speed • Some DAX functions are not supported • Limited relationship and modeling options • Can create heavy load on source systems • Maximum of 1 million rows returned per query
Key Limitations of Import:
• Data is only as fresh as the last refresh • Dataset size limits apply • Refresh operations consume resources • Scheduled refresh limits per day
Composite Models:
Power BI allows combining both modes in a single model. You can import some tables while using DirectQuery for others, providing flexibility to optimize for both performance and data freshness.
Exam Tips: Answering Questions on Choose between DirectQuery and Import
Tip 1: When a question mentions real-time data requirements or data that must be current at all times, DirectQuery is typically the answer.
Tip 2: If the scenario describes performance concerns or the need for complex calculations, Import mode is usually preferred.
Tip 3: Look for keywords like row-level security at the source or database-level security — these point toward DirectQuery.
Tip 4: Questions mentioning dataset size limits or very large datasets often indicate DirectQuery as the solution.
Tip 5: When multiple data sources must be combined or related together, Import mode provides more flexibility.
Tip 6: Pay attention to refresh requirements — if hourly or daily refresh is acceptable, Import is viable; if up-to-the-minute data is needed, consider DirectQuery.
Tip 7: Remember that DirectQuery queries are translated to the native query language of the source, which affects which transformations are supported.
Tip 8: For exam scenarios involving slow report performance with DirectQuery, solutions often involve aggregations or switching specific tables to Import mode using composite models.