Trees are immutable, and TreeNode takes care of copying unchanged parts of
the tree when you are doing transformations. As a result, even if you do
construct a DAG with the Dataset API, the first transformation will turn it
back into a tree.
The only exception to this rule is when we share the
i am trying to understand some parts of the catalyst optimizer. but i
struggle with one bigger picture issue:
LogicalPlan extends TreeNode, which makes sense since the optimizations
rely on tree transformations like transformUp and transformDown.
but how can a LogicalPlan be a tree? isnt it
