Introduction
Power BI provides different ways to connect to data, known as storage modes. The three most common options are Import, DirectQuery, and Composite models. Choosing the right mode is especially important when working with large datasets, real-time data, or enterprise systems.
Many performance issues in Power BI are not caused by visuals or DAX, but by selecting the wrong storage mode. This article explains Import, DirectQuery, and Composite models in simple words, how they work in real-world scenarios, and when each option makes sense.
What Import Mode Is
In Import mode, data is loaded into Power BI’s in-memory engine. Once imported, reports interact with this in-memory data rather than querying the source system each time.
This makes Import mode very fast for filtering, slicing, and interacting with visuals. However, data is only as fresh as the last refresh.
For example, a sales dashboard refreshed every morning uses Import mode to deliver very fast report performance throughout the day.
Advantages of Import Mode
Import mode offers the best performance for most reports. Queries are processed in memory, which makes visuals load quickly.
It also supports complex DAX calculations efficiently and works well with large but manageable datasets.
For example, historical reporting and executive dashboards usually perform best in Import mode.
Limitations of Import Mode
The main limitation of Import mode is data freshness. Changes in the source system are not visible until the next refresh.
Large datasets may also hit memory or size limits if not optimized.
For example, importing billions of rows without aggregation can lead to slow refreshes or dataset size issues.
What DirectQuery Mode Is
In DirectQuery mode, Power BI does not store data locally. Instead, it sends queries directly to the source system whenever a user interacts with a report.
This allows near real-time access to data but shifts the performance responsibility to the data source.
For example, monitoring dashboards connected to live operational databases often use DirectQuery.
Advantages of DirectQuery Mode
DirectQuery provides up-to-date data without waiting for scheduled refreshes. It also avoids storing large datasets inside Power BI.
This mode is useful when data changes frequently or must always be current.
For example, real-time inventory or monitoring dashboards benefit from DirectQuery.
Limitations of DirectQuery Mode
DirectQuery reports are usually slower than Import mode because every interaction triggers a query to the source system.
Performance depends on database design, indexing, network latency, and concurrent load.
For example, a poorly indexed database can make DirectQuery reports feel slow and unresponsive.
What Composite Models Are
Composite models combine Import and DirectQuery in a single Power BI dataset. Some tables are imported, while others use DirectQuery.
This approach balances performance and data freshness.
For example, historical sales data can be imported, while today’s transactions are queried in real time.
Advantages of Composite Models
Composite models provide flexibility. Frequently used historical data remains fast, while real-time data stays current.
They also reduce load on source systems compared to full DirectQuery.
For example, executives can analyze trends quickly while still seeing up-to-date operational metrics.
Challenges with Composite Models
Composite models are more complex to design and maintain. Developers must carefully manage relationships, filters, and performance expectations.
Incorrect configuration can lead to unexpected slowdowns.
For example, joining large DirectQuery tables with imported tables without optimization can hurt performance.
How to Choose the Right Model
Choosing the right storage mode depends on data size, freshness requirements, and performance expectations.
Import mode suits most analytical and reporting use cases. DirectQuery fits real-time or very large datasets. Composite models work best when both speed and freshness are required.
For example, combining Import mode with Incremental Refresh often delivers excellent results for large enterprise datasets.
Summary
Import, DirectQuery, and Composite models each solve different problems in Power BI. Import mode delivers the best performance for most reports, DirectQuery enables real-time access at the cost of speed, and Composite models offer a balanced approach. Understanding these differences helps teams design Power BI solutions that scale well, perform reliably, and meet business needs without unnecessary complexity.