Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21072#discussion_r183382434
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -736,12 +736,29 @@ object EliminateSorts extends Rule[LogicalPlan] {
}
/**
- * Removes Sort operation if the child is already sorted
+ * Removes redundant Sort operation. This can happen:
+ * 1) if the child is already sorted
+ * 2) if there is another Sort operator separated by 0...n Project/Filter
operators
*/
object RemoveRedundantSorts extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
--- End diff --
nit: now it's more efficient to do `transformDown`
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