In a dataflow, which transformation steps will fold?

In the context of dataflows, the term "folding" refers to a process where certain transformations can be pushed down to the data source rather than being performed in-memory or via intermediate steps within the dataflow. This is particularly significant for performance optimization, as it allows for more efficient data retrieval.

Some transformations are foldable, meaning that they can be translated into SQL or other language queries that the source database can execute. This includes operations like filtering, aggregating, and joining data. However, not every transformation can be folded; for instance, complex transformations or those involving custom functions may not be supported.

Selecting "some" as the answer acknowledges that while a portion of the transformations can be pushed to the data source to improve efficiency, there are limitations on which specific transformations can engage in this folding process. This variability reflects the diverse capabilities and constraints of different data sources and transformation types, thereby affirming that folding applies selectively rather than universally across all transformations.