maropu commented on a change in pull request #31691:
URL: https://github.com/apache/spark/pull/31691#discussion_r585204557
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -613,6 +613,15 @@ object LimitPushDown extends Rule[LogicalPlan] {
case _ => join
}
LocalLimit(exp, newJoin)
+
+ case LocalLimit(limitExpr @ IntegerLiteral(limitVal),
+ window @ Window(Seq(Alias(WindowExpression(_: RankLike | _: RowNumber,
+ WindowSpecDefinition(Nil, orderSpec,
+ SpecifiedWindowFrame(RowFrame, UnboundedPreceding,
CurrentRow))), _)), _, _, child))
+ if child.maxRows.forall( _ > limitVal) =>
+ LocalLimit(
+ limitExpr = limitExpr,
+ child = window.copy(child = Limit(limitExpr, Sort(orderSpec, true,
child))))
Review comment:
If no partitionSpec specified, I think the planner inserts an exchange
for making a single partition. So, we don't need a global sort here?
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