maropu commented on a change in pull request #30368:
URL: https://github.com/apache/spark/pull/30368#discussion_r522963158
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -1452,11 +1452,23 @@ object PushPredicateThroughJoin extends
Rule[LogicalPlan] with PredicateHelper {
}
/**
- * Combines two adjacent [[Limit]] operators into one, merging the
- * expressions into one single expression.
+ * 1. Eliminate [[Limit]] operators if it's child max row <= limit.
+ * 2. Combines two adjacent [[Limit]] operators into one, merging the
+ * expressions into one single expression.
*/
-object CombineLimits extends Rule[LogicalPlan] {
- def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+object EliminateLimits extends Rule[LogicalPlan] {
+ private def canEliminate(limitExpr: Expression, childMaxRow: Option[Long]):
Boolean = {
+ limitExpr.foldable &&
+ childMaxRow.isDefined &&
+ childMaxRow.get <= limitExpr.eval().toString.toInt
Review comment:
I'm not a jvm expert, but jvm implicitly coerces the type into long in
the comparison? If so, I think it is a bit efficient to convert it into long
directly.
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