datasource change taking forever

[Anonymous]

I have a power bi report that has oracle as source, i just changed the connection from production to a test environment schema, in data source settings, then hit apply changes, i see the attached message and its just says evaluating ....

what is happening behind the scenes and why is it taking forever ?

[lbendlin · Accepted solution]

When you changed the connection Power BI panicked and threw away all the meta data it had accumulated for the prior setup. Now it is starting over and collecting all the meta data anew. I really wish they would find a better way to do this.

[Anonymous]

Thank you, what exactly is "metadata" and where can I get more information about it ?

[lbendlin]

It is information about the structure of the data, rather than the data itself. So it lists field types, field sizes, indexes, relationship keys etc. A semantic layer, if you will.

[Anonymous]

Is there a place that I can see this information ?

[lbendlin]

Check the Power Query Value.* functions like

Value.Metadata - PowerQuery M | Microsoft Docs

Value.Is - PowerQuery M | Microsoft Docs

Value.Type - PowerQuery M | Microsoft Docs

Also, Ben Gribaudo has an excellent series of articles about the darker corners of Power Query, including Metadata.

https://bengribaudo.com/blog/2017/11/17/4107/power-query-m-primer-part1-introduction-simple-expressi...