Performance Test: Loading CSV Versus Loading Excel In Power Query

Chris Webb lays out a performance test which shows how quickly Power Query can read data from a CSV versus from an Excel spreadsheet:

The black line in the graph above is the amount of data read (actually the offset values showing where in the file the data is read from, which is the same thing as a running total when Power Query is reading all the data) from the Excel file; the green line is the amount of data read from the CSV file (the same data shown in the first graph above). A few things to mention:

  • Running Process Monitor while this second query was refreshing had a noticeable impact on its performance – in fact it was almost 20 seconds slower

  • The initial values of 80 million bytes seem to be where data is read from the end of the Excel file. Maybe this is Power Query reading some file metadata? Anyway, it seems as though it takes 5 seconds before it starts to read the data needed by the query.

  • There’s a plateau between the 10 and 20 second mark where not much is happening; this didn’t happen consistently and may have been connected to the fact that Process Monitor was running

The results were remarkable; check them out.

Related Posts

Removing Text Between Delimiters in Power Query

Imke Feldmann has a new M function for us: While there is a native function to fetch text between 2 delimiters in Power Query, there is no such function that removes the text instead. Therefore I’ve created a custom function Text.RemoveBetweenDelimiter. It even lets you choose to remove the delimiters themselves as well via the […]

Read More

Power BI Pareto Charts

Matt Allington shows how you can build up a Pareto chart in Power BI: Pareto Analysis is a statistical technique that applies the Pareto Principle to data. This is more commonly known as the 80:20 Rule. The Pareto Principle is based on the presumption that a relatively small number of inputs (20%)  have most impact […]

Read More

Categories

August 2018
MTWTFSS
« Jul Sep »
 12345
6789101112
13141516171819
20212223242526
2728293031