Darren Gosbell

Tag: paginated-reports

Diagnosing Performance of Paginated Reports in Power BI

Sometimes when you have a slow paginated report it’s hard to know where to start in order to improve the performance.

There is a feature in Paginated Reports on the Power BI service that was released a number of months ago which will show you a breakdown of the performance of that report.

After you have run your report you can access this feature by going into the View menu and clicking on the Diagnostics button

The Paginated Report Diagnostics dialog

Power BI Report Server and SQL Server Reporting Services do not have this button on the report itself, but you can get the same timing information by querying the ExecutionLog3 view in the ReportServer database (see Report Server ExecutionLog and the ExecutionLog3 View – SQL Server Reporting Services (SSRS) | Microsoft Learn)

This dialog shows us a number of pieces of interesting information about the report execution.

  1. Note the item at the top here which says “Capacity throttled = no” this applies to premium capacities and tells you if the capacity is currently in a throttled state. This is important as throttling adds a delay to interactive operations like report rendering and so your report may have slow performance because previous operations on the capacity have put it into a throttled state.
  2. This second section of the report shows you a breakdown of the different category of operations in the report as well as a count of the total dataset rows that were processed.

If you want to understand what is happening during each step of the performance metrics, I found the following information in this archived blog post from a former member of the SSRS team which breaks down the operations which go into each of these 3 categories.

Data Retrieval Time

The number of milliseconds spent interacting with data sources and data extensions for all data sets in the main report and all of its subreports. This value includes:

  • Time spent opening connections to the data source
  • Time spent reading data rows from the data extension

Note: If a report has multiple data sources/data sets that can be executed in parallel, TimeDataRetrieval contains the duration of the longest DataSet, not the sum of all DataSets durations. If DataSets are executed sequentially, TimeDataRetrieval contains the sum of all DataSet durations.

Processing Time

The number of milliseconds spent in the processing engine for the request. This value includes:

  • Report processing bootstrap time
  • Tablix processing time (e.g. grouping, sorting, filtering, aggregations, subreport processing), but excludes on-demand expression evaluations (e.g. TextBox.Value, Style.*)
  • ProcessingScalabilityTime**

Rendering Time

The number of milliseconds spent after the Rendering Object Model is exposed to the rendering extension. This value includes:

  • Time spent in renderer
  • Time spent in pagination modules
  • Time spent in on-demand expression evaluations (e.g. TextBox.Value, Style.*). This is different from prior releases, where TimeProcessing included all expression evaluation.
  • PaginationScalabilityTime**
  • RenderingScalabilityTime**

** The “scalability” times are when the engine does extra operations to free up memory in response to memory pressure issues during processing, pagination or rendering

Optimizing Report Performance

If you are interested in ways to optimize the performance of a paginated report, then many of the techniques outlined in this old article are still perfectly valid even though it was written for SQL 2008R2 – you can just ignore some of the points that are specific to on-prem scenarios like point 2 using Shared Data Sources which are not available in the Power BI service.

Logging Parameters for a Paginated Report

If you look at the Power BI audit logs for paginated reports you can see which user ran which report and when, but you cannot see any parameter values. This is by-design since parameter values are considered “customer content” and no content like this is included in the Power BI logs.

But if your company has a requirement to log which parameter values were used when running a report then this is something you will need to build yourself.

One possible way of doing this is to add a dataset to your report which does an insert command or calls a stored procedure to insert a record into a custom audit table.

I did this using Azure SQL and creating the following table:

CREATE TABLE [dbo].[ReportExecutionLog](
	[ReportName] [nvarchar](255) NULL,
	[UserName] [nvarchar](255) NULL,
	[Parameters] [nvarchar](max) NULL,
	[DateTime] [datetime] NULL

And the following Stored Procedure:

CREATE PROC [dbo].[sprInsertLogRecord]( @reportName NVARCHAR(255), 
                                        @userName NVARCHAR(255), 
                                        @params NVARCHAR(MAX))
INSERT INTO [dbo].[ReportExecutionLog]

Then I added a connection to my Azure SQL database in Report Builder and created a new dataset called “Logging” and configured it to call this stored procedure.

Then in the parameters section I set it up to pass in the global ReportName and UserID values

Note: Unfortunately there is currently no way to get the ReportID or WorkspaceID, hopefully this gets added at some point in the future. For the time being this means that you need to make sure that any reports you want to add logging to must have unique names. You could possibly look at adding some unique report ID to your report name to ensure this.

In the screenshot above you can see that there is an expression for the parameter values that I want to capture, this is calling a small custom function. The code in the expression is as follows and I’m just passing in an array of the parameter name that I want to log:

The GetParameterValues function is as follows:

Public Function GetParameterValues( ByVal paramsToLog As Array) As String
	Dim params as String
	Dim i as Integer
	Dim pName as String

	For Each pName in paramsToLog
		Dim p as Parameter
		p = Report.Parameters(pName)
		Dim pVal as String
		If (p.Count > 1) Then
			pVal = Join(p.Value, ",")
			pVal = p.Value
		End If	

		params = params & pName & "=" & pVal & vbCrLf	
	Next pName

	Return params
End Function

I entered this in the “Code” property for the report by clicking in the dark gray background area to expose the report level properties

Then when you click on the … button to edit the code value I paste the code into the “Custom code” area.

This then produces output like the following.

Note that in my function I am using a newline between each parameter which SSMS does not show in it’s grid output, but you can see them if you build a report over this log table. If you want to a different delimiter between the parameters you could simply replace the vbCrLf value in the function above with something else.