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Simulating Slow Data Sources in Power BI

Chris Webb builds a particular kind of test:

As a postscript to my series on Power BI refresh timeouts (see part 1part 2 and part 3) I thought it would be useful to document how I was able to simulate a slow data source in Power BI without using large data volumes or deliberately complex M code.

It’s relatively easy to create an M query that returns a table of data after a given delay. For example, this query returns a table with one column and one row after one hour and ten minutes:

Read on for a version of the function which slowly emits rows, as well as some T-SQL which slowly emits rows.