cloud-fan commented on code in PR #36417:
URL: https://github.com/apache/spark/pull/36417#discussion_r866824230
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala:
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@@ -1871,21 +1874,18 @@ object EliminateLimits extends Rule[LogicalPlan] {
}
/**
- * Rewrite [[Offset]] as [[GlobalLimitAndOffset]] or [[LocalLimit]],
- * merging the expressions into one single expression. See [[Limit]] for more
information
- * about the difference between [[LocalLimit]] and [[GlobalLimit]].
+ * This rule optimizes Offset operators by:
+ * 1. Eliminate [[Offset]] operators if offset == 0.
+ * 2. Replace [[Offset]] operators to empty [[LocalRelation]]
+ * if [[Offset]]'s child max row <= offset.
*/
-object RewriteOffsets extends Rule[LogicalPlan] {
+object EliminateOffsets extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
- case GlobalLimit(le, Offset(oe, grandChild)) =>
- GlobalLimitAndOffset(le, oe, grandChild)
- case localLimit @ LocalLimit(le, Offset(oe, grandChild)) =>
- val offset = oe.eval().asInstanceOf[Int]
- if (offset == 0) {
- localLimit.withNewChildren(Seq(grandChild))
- } else {
- Offset(oe, LocalLimit(Add(le, oe), grandChild))
- }
+ case Offset(oe, child) if oe.foldable && oe.eval().asInstanceOf[Int] == 0
=>
+ child
+ case Offset(oe, child)
+ if oe.foldable && child.maxRows.exists(_ <= oe.eval().asInstanceOf[Int])
=>
+ LocalRelation(child.output, data = Seq.empty, isStreaming =
plan.isStreaming)
Review Comment:
```suggestion
LocalRelation(child.output, data = Seq.empty, isStreaming =
child.isStreaming)
```
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