Github user henryr commented on a diff in the pull request:
https://github.com/apache/spark/pull/21072#discussion_r181563918
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -736,12 +736,15 @@ 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 the next operator is a Sort itself
*/
object RemoveRedundantSorts extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
case Sort(orders, true, child) if
SortOrder.orderingSatisfies(child.outputOrdering, orders) =>
child
+ case s @ Sort(_, _, Sort(_, _, child)) => s.copy(child = child)
--- End diff --
Thanks for doing this! It might be useful to generalise this to any pair of
sorts separated by 0 or more projections or filters. I did this for my
SPARK-23975 PR, see:
https://github.com/henryr/spark/commit/bb992c2058863322a9183b2985806a87729e4168#diff-a636a87d8843eeccca90140be91d4fafR322
What do you think?
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