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Data retrieval guidance for paginated reports

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This article targets you as a report author designing Power BI paginated reports. It provides recommendations to help you design effective and efficient data retrieval.

Data source types

Paginated reports natively support both relational and analytic data sources. These sources are further categorized, as either cloud-based or on-premises. On-premises data sources—whether hosted on-premises, or in a virtual machine—require a data gateway so Power BI can connect. Cloud-based means that Power BI can connect directly using an Internet connection.

If you can choose the data source type (possibly the case in a new project), we recommend that you use cloud-based data sources. Paginated reports can connect with lower network latency, especially when the data sources reside in the same region as your Power BI tenant. Also, it's possible to connect to these sources by using Single Sign-On (SSO). It means the report user's identity can flow to the data source, allowing per-user row-level permissions to be enforced. Currently, SSO is only supported for on-premises data sources SQL Server and Oracle (see Supported data sources for Power BI paginated reports).

Note

While it's currently not possible to connect to on-premises databases using SSO, you can still enforce row-level permissions. It's done by passing the UserID built-in field to a dataset query parameter. The data source will need to store User Principal Name (UPN) values in a way that it can correctly filter query results.

For example, consider that each salesperson is stored as a row in the Salesperson a table. The table has columns for UPN, and also the salesperson's sales region. At query time, the table is filtered by the UPN of the report user, and it's also related to sales facts using an inner join. This way, the query effectively filters sales fact rows to those of the report user's sales region.

Relational data sources

Generally, relational data sources are well suited to operational style reports, like sales invoices. They're also suited for reports that need to retrieve very large datasets (in excess of 10,000 rows). Relational data sources can also define stored procedures, which can be executed by report datasets. Stored procedures deliver several benefits:

  • Parameterization
  • Encapsulation of programming logic, allowing for more complex data preparation (for example, temporary tables, cursors, or scalar user-defined functions)
  • Improved maintainability, allowing stored procedure logic to be easily updated. In some cases, it can be done without the need to modify and republish paginated reports (providing column names and data types remain unchanged).
  • Better performance, as their execution plans are cached for reuse
  • Reuse of stored procedures across multiple reports

In Power BI Report Builder, you can use the relational query designer to graphically construct a query statement—but only for Microsoft data sources.

Analytic data sources

Analytic data sources—also known as data models or just models—are well suited to both operational and analytic reports, and can deliver fast summarized query results even over very large data volumes. Model measures and KPIs can encapsulate complex business rules to achieve summarization of data. These data sources, however, aren't suited to reports that need to retrieve very large volumes of data (in excess of 10,000 rows).

In Power BI Report Builder, you have a choice of two query designers: The Analysis Services DAX query designer, and the Analysis Services MDX query designer. These designers can be used for Power BI semantic model (previously known as a dataset) data sources, or any SQL Server Analysis Services or Azure Analysis Services model—tabular or multidimensional.

We recommend that you use the DAX query designer—providing it entirely meets your query needs. If the model doesn't define the measures you need, you'll need to switch to query mode. In this mode, you can customize the query statement by adding expressions (to achieve summarization).

The MDX query designer requires your model to include measures. The designer has two capabilities not supported by the DAX query designer. Specifically, it allows you to:

  • Define query-level calculated members (in MDX).
  • Configure data regions to request server aggregates in non-detail groups. If your report needs to present summaries of semi- or non-additive measures (like time intelligence calculations, or distinct counts), it will likely be more efficient to use server aggregates than to retrieve low-level detail rows and have the report compute summarizations.

Query result size

In general, it's best practice to retrieve only the data required by your report. So, don't retrieve columns or rows that aren't required by the report.

To limit rows, you should always apply the most restrictive filters, and define aggregate queries. Aggregate queries group and summarize source data to retrieve higher-grain results. For example, consider that your report needs to present a summary of salesperson sales. Instead of retrieving all sales order rows, create a dataset query that groups by salesperson, and summarizes sales for each group.

Expression-based fields

It's possible to extend a report dataset with fields based on expressions. For example, if your dataset sources customer first name and last name, you might want a field that concatenates the two fields to produce the customer full name. To achieve this calculation, you have two options. You can:

  • Create a calculated field, which is a dataset field based on an expression.
  • Inject an expression directly into the dataset query (using the native language of your data source), which results in a regular dataset field.

We recommend the latter option, whenever possible. There are two good reasons why injecting expressions directly into your dataset query is better:

  • It's possible your data source is optimized to evaluate the expression more efficiently than Power BI (it's especially the case for relational databases).
  • Report performance is improved because there's no need for Power BI to materialize calculated fields prior to report rendering. Calculated fields can noticeably extend report render time when datasets retrieve a large number of rows.

Field names

When you create a dataset, its fields are automatically named after the query columns. It's possible these names aren't friendly or intuitive. It's also possible that source query column names contain characters prohibited in Report Definition Language (RDL) object identifiers (like spaces and symbols). In this case, the prohibited characters are replaced with an underscore character (_).

We recommend that you first verify that all field names are friendly, concise, yet still meaningful. If not, we suggest you rename them before you commence the report layout. It's because renamed fields don't ripple changes through to the expressions used in your report layout. If you do decide to rename fields after you've commenced the report layout, you'll need to find and update all broken expressions.

Filter vs parameter

It's likely that your paginated report designs will have report parameters. Report parameters are commonly used to prompt your report user to filter the report. As a paginated report author, you have two ways to achieve report filtering. You can map a report parameter to:

  • A dataset filter, in which case the report parameter value(s) are used to filter the data already retrieved by the dataset.
  • A dataset parameter, in which case the report parameter value(s) are injected into the native query sent to the data source.

Note

All report datasets are cached on a per-session basis for up to 10 minutes beyond their last use. A dataset can be re-used when submitting new parameter values (filtering), rendering the report in a different format, or interacting with the report design in some way, like toggling visibility, or sorting.

Consider, then, an example of a sales report that has a single report parameter to filter the report by a single year. The dataset retrieves sales for all years. It does so because the report parameter maps to the dataset filters. The report displays data for the requested year, which is a subset of the dataset data. When the report user changes the report parameter to a different year—and then views the report—Power BI doesn't need to retrieve any source data. Instead, it applies a different filter to the already-cached dataset. Once the dataset is cached, filtering can be very fast.

Now, consider a different report design. This time the report design maps the sales year report parameter to a dataset parameter. This way, Power BI injects the year value into the native query, and the dataset retrieves data only for that year. Each time the report user changes the year report parameter value—and then views the report—the dataset retrieves a new query result for just that year.

Both design approaches can filter report data, and both designs can work well for your report designs. An optimized design, however, will depend on the anticipated volumes of data, data volatility, and the anticipated behaviors of your report users.

We recommend dataset filtering when you anticipate a different subset of the dataset rows will be reused many times (thereby saving rendering time because new data doesn't need to be retrieved). In this scenario, you recognize that the cost of retrieving a larger dataset can be traded off against the number of times it will be reused. So, it's helpful for queries that are time consuming to generate. But take care—caching large datasets on a per-user basis may negatively impact on performance, and capacity throughput.

We recommend dataset parameterization when you anticipate it's unlikely that a different subset of dataset rows will be requested—or, when the number of the dataset rows to be filtered is likely to be very large (and inefficient to cache). This design approach work well, too, when your data store is volatile. In this case, each report parameter value change will result in the retrieval of up-to-date data.

Non-native data sources

If you need to develop paginated reports based on data sources that aren't natively supported by paginated reports, you should first develop a data model in Power BI Desktop. That way, you can connect to hundreds of data sources supported by Power BI. Once published to the Power BI service, you can then develop a paginated report that connects to the Power BI semantic model.

Data integration

If you need to combine data from multiple data sources, you have two options:

  • Combine report datasets: If the data sources are natively supported by paginated reports, you can consider creating calculated fields that use the Lookup or LookupSet Report Builder functions.
  • Develop a Power BI Desktop model: It's likely more efficient, however, that you develop a data model in Power BI Desktop. You can use Power Query to combine queries based on any supported data source. Once published to the Power BI service, you can then develop a paginated report that connects to the Power BI semantic model.

Network latency

Network latency can impact report performance by increasing the time required for requests to reach the Power BI service, and for responses to be delivered. Tenants in Power BI are assigned to a specific region.

Tip

To determine where your tenant is located, see Where is my Power BI tenant located?

When users from a tenant access the Power BI service, their requests always route to this region. As requests reach the Power BI service, the service may then send additional requests—for example, to the underlying data source, or a data gateway—which are also subject to network latency. In general, to minimize the impact of network latency, strive to keep data sources, gateways, and your Power BI capacity as close as possible. Preferably, they reside within the same region. If network latency is an issue, try locating gateways and data sources closer to your Power BI capacity by placing them inside cloud-hosted virtual machines.

SQL Server complex data types

Because SQL Server is an on-premises data source, Power BI must connect via a gateway. The gateway, however, doesn't support retrieving data for complex data types. Complex data types include built-in types like the GEOMETRY and GEOGRAPHY spatial data types, and hierarchyid. They can also include user-defined types implemented through a class of an assembly in the Microsoft.NET Framework common language runtime (CLR).

Plotting spatial data and analytics in the map visualization requires SQL Server spatial data. Therefore, it's not possible to work with the map visualization when SQL Server is your data source. To be clear, it will work if your data source is Azure SQL Database because Power BI doesn't connect via a gateway.

Images can be used to add logos or pictures to your report layout. When images relate to the rows retrieved by a report dataset, you have two options:

  • It's possible that image data can also be retrieved from your data source (if already stored in a table).
  • When the images are stored on a web server, you can use a dynamic expression to create the image URL path.

For more information and suggestions, see Image guidance for paginated reports.

Redundant data retrieval

It's possible your report retrieves redundant data. This can happen when you delete dataset query fields, or the report has unused datasets. Avoid these situations, as they result in an unnecessary burden on your data sources, the network, and Power BI capacity resources.

Deleted query fields

On the Fields page of the Dataset Properties window, it's possible to delete dataset query fields (query fields map to columns retrieved by the dataset query). However, Report Builder doesn't remove corresponding columns from the dataset query.

If you need to delete query fields from your dataset, we recommend you remove the corresponding columns from the dataset query. Report Builder will automatically remove any redundant query fields. If you do happen to delete query fields, be sure to also modify the dataset query statement to remove the columns.

Unused datasets

When a report is run, all datasets are evaluated—even if they're not bound to report objects. For this reason, be sure to remove any test or development datasets before you publish a report.

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