SSRS 2017 reports loading slow on first time

Hi @venkateswararao ,
According to your description , it seems could related to the below 2 aspects :

1 What the certification you use in the datasource connection? data base credentials or service credentials?

2 it could cause by the ssrs sleep function .
Reporting services in native mode start slowly after some time of inactivity if you render using report viewer control from report server. In other words, after a period of inactivity SSRS "falls asleep" and on the next (first) Report Access it takes some time until SSRS is up again.You can change settings of reporting services so that they fall asleep after longer period of time. Description here
or I suggest you can warm up your web service using script.Someone tested this and it works really well. Click here to view information about RS.exe utility (SSRS).

Script file "RunReport.rss"

Public Sub Main()  
  
  Dim format as string = "PDF"  
  Dim fileName as String  
  ' adapt the following variable for your report location  
  Dim reportPath as String = "/{my file path}/{my report name}"  
  
  Dim parameters(0) As ParameterValue  
  
  ' Prepare Render arguments  
  Dim historyID as string = Nothing  
  Dim deviceInfo as string = Nothing  
  Dim extension as string = Nothing  
  Dim encoding as string  
  Dim mimeType as string  
  Dim warnings() AS Warning = Nothing  
  Dim streamIDs() as string = Nothing  
  Dim results() as Byte  
  
  
  rs.LoadReport(reportPath, historyID)  
  
  fileName = "output.pdf"  
  
  results = rs.Render(format,  deviceInfo, extension, _  
  mimeType, encoding,  warnings, streamIDs)  
  
  ' Open a file stream and write out the report  
  Dim stream  As FileStream = File.OpenWrite(fileName)  
  stream.Write(results, 0, results.Length)  
  stream.Close()  
  
End Sub  

Which is then executed from the command line with

rs -i RunReport.rss -s http://{my server name}/reportserver -t -e Exec2005  

And in this case creates a file called "output.pdf"
Hopefully that may be of use.
Regards，
Joy

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