Custom table visual max allowed size

Hi Anonymous,

The data reduction algorithm should apply a TOPN in the generated query in the DAX that is generated by Power BI, but it would look like adding the dimension causes some issue with either the query that Power BI generates on your visual's behalf (or the query that Power BI does from the DAX to the back-end). It may need to get more information from the remote data source and this could be breaking the row limit that DirectQuery has. As the data reduction algorithm is the only means you have to limit the outgoing query from a custom visual, this may be a "feature" of DirectQuery and/or how Power BI accesses your data in this scenario.

The easiest thing to do would be to see if you can profile both the DAX being generated by your visual (through Performance Analyzer) and the query being run against Databricks and see what the resulting dataset looks like (I don't have much experience on this part to advise how to do it). If this is >1M rows, then it suggests that this is indeed a DirectQuery-related scenario. FWIW if you can replicate this with the core table visual, it may reinforce the limitation, as this visual has its own data reduction algorithm and will paginate additional queries after the first query has returned its data.