Scheduled Refresh / Preparing A Refresh - What happens to the existing data?

[danielpaduck]

Hi,

What exactly happens when Power BI is 'Preparing a Refresh'. Does Power BI drop all of the data from the workbook and then reloads it? I ask this because I have several users that indicated some data is missing at certain times of the day.  I think it is because they are logging in and looking at the Power BI report during a refresh.  

As an aside - I don't think I had this issue with Tableau. 

Thanks!

[m-colbert · Accepted solution]

@danielpaduck 

I was on with Microsoft engineer this am and he confirmed that when a dataset refresh is issued, the service make a copy of the dataset to be sure 1) there is a copy in case the refresh fails and 2) to support the report viewing during the refresh until it's completed.

I have seen some odd behavior around refreshes that required a reset to default or refresh the broser to re-load the entire report. 

Hope this helps.

[danielpaduck]

To confirm - when the refresh completes then Power BI will essentially swap out the data? Therefore, it should be seemless between a data set that was populated yesterday versus today's (current) data set?  

Thanks!

[danielpaduck]

One of my collegues thinks that Power BI will delete all of the day and then do a rolling import of the data. Thus, let's say you are import employee time sheet data by employee's last name.  Those whose last name start with 'A' will be available in the report before those those last name start with 'Z'. 

[danielpaduck]

Hi - the data source is SQL Server.  The data set/table could contain close to million rows. Thus, the refresh takes several minutes.  The refresh will finish it is just that if a user comes in during a refresh then they are not seeing all of the data until the refresh is completely done.  I just want to confirm that Power BI will delete the entire data set before loading, then starting loading and presenting whatever data is available (has been consumed by the refresh). 

[m-colbert]

@danielpaduck 

What is your data source? Power BI is designed to rollback any failures and the dataset left intact during refreshes. So this seems odd that you would be missing data form the dataset itself. Is this repeatable?

Thanks