Query Folding

Devin Knight discusses query folding and the View Native Query feature inside Power Query:

The idea behind Query Folding is to push the logic that you built into a Power BI query back to the data source server and execute it there in it’s native language instead of doing a client side transform of the data.  Why is this important?  Let me give you an example.  Say you have a 2 billion row SQL Server table you need to connect to in Power BI, but you want to filter to only return the last year of data.  With Query Folding the filter of that data is done on the SQL Server side instead of on the client side. If Query folding did not take place than that would mean all 2 billion rows would be brought across the network only to then filtered out on the client workstation.  So clearly the ideal situation is that all your queries get folded for the best possible performance, but Query Folding only works in certain scenarios.

I hadn’t heard the term “query folding” before, but the concept makes sense; in the PolyBase world, it’s “predicate pushdown.”  Check out Devin’s post, as he shows how easy it is to see to what extent your query is running client-side versus server-side.

Related Posts

Storing Large Images in Power BI

Chris Webb shows us how to store a large image in Power BI: Jason Thomas and Gerhard Brueckl have both blogged on the subject of storing images as text inside a Power BI dataset:http://sqljason.com/2018/01/embedding-images-in-power-bi-using-base64.htmlhttps://blog.gbrueckl.at/2018/01/storing-images-powerbi-analysis-services-data-models/ Since they wrote those posts, however, Power BI has added the ability to set the Data Category property on measures as […]

Read More

Power BI Connection String Capitalization

Slava Murygin ran into a problem with capitalization on connection strings with Power BI Report Server: The message actually says:“Several errors occurred during data refresh. Please try again later or contact your administrator.”SessionID: 1b80301e-3898-417a-af9c-2e77ec490728[0] -1055784932: Credentials are required to connect to the SQL source. (Source at SQLServerName;DBA_Pro.). The exception was raised by the IDbCommand interface.[1] […]

Read More

Categories

July 2016
MTWTFSS
« Jun Aug »
 123
45678910
11121314151617
18192021222324
25262728293031