Github user scwf commented on a diff in the pull request:
https://github.com/apache/spark/pull/5821#discussion_r29487480
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -618,6 +618,9 @@ object CombineLimits extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
case ll @ Limit(le, nl @ Limit(ne, grandChild)) =>
Limit(If(LessThan(ne, le), ne, le), grandChild)
+
+ case s @ Sort(_, _, Limit(exp, grandChild)) =>
--- End diff --
My bad, after thinking more about this, i think we can not add this rule,
because push down sort leads to sort global data.
But here is another case we can optimize, i am updating this.
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