What is the best way to vertically combine two large tables of the same structure. Each table is about 2 mln rows. Is there any performance advantage to do it in M, not in DAX?
M approach
BigTable_M = Table.Combine( {Table1, Table2} )
DAX approach
BigTable_DAX = UNION ( 'Table1', 'Table2' )
I have a feeling that M way loads the tables two times. Separately each primary source (Table1 and Table2) and then again both tables while loading rows to BigTable_M. Is there any reason to suffer this double load for better performance later?
By this article it seems that M is faster.
https://www.sqlbi.com/articles/comparing-dax-calculated-columns-with-power-query-computed-columns/