Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/11480#discussion_r54840644
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -483,6 +484,25 @@ object CollapseRepartition extends Rule[LogicalPlan] {
}
/**
+ * Collapse two adjacent [[Sort]] operators into one if possible. Keep the
last sort
+ * This rule applies to the scenario where the global is same for the Sort
nodes and then
+ * either a) The sorts are adjacent or b) In between two Sort nodes, there
is a Filter or
+ * a Project or a Limit
+ */
+object CollapseSorts extends Rule[LogicalPlan] {
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
--- End diff --
as it is, i'm not sure how useful this rule is.
I think what would be useful is to have an EliminateSort rule, that can
actually eliminate the more useful cases.
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