Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/10577#discussion_r48820132
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -595,6 +598,22 @@ object BooleanSimplification extends Rule[LogicalPlan]
with PredicateHelper {
}
/**
+ * Combines all adjacent [[Union]] and [[Unions]] operators into a single
[[Unions]].
+ */
+object CombineUnions extends Rule[LogicalPlan] {
+ private def collectUnionChildren(plan: LogicalPlan): Seq[LogicalPlan] =
plan match {
+ case Union(l, r) => collectUnionChildren(l) ++ collectUnionChildren(r)
--- End diff --
Another option would just be to do this at construction time, that way we
can avoid paying the cost in the analyzer. This would still limit the cases we
could cache (i.e. we'd miss cached data unioned with other data), but that
doesn't seem like a huge deal.
I'd leave this rule here either way.
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