Optimizing nested iterators in DAX
One of the possible causes of slow performance in DAX is the presence of nested iterators in an expression. The real issue is not the presence of an iterator by itself, but the cardinality of the materialization required by the lowest level of context transition. While it is true that moving most of the workload to the storage engine is a good idea, finding the right balance between materialization and storage engine calculation is the ultimate goal.