maropu commented on a change in pull request #30368: URL: https://github.com/apache/spark/pull/30368#discussion_r524811988
########## File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala ########## @@ -1452,11 +1452,27 @@ 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, child: LogicalPlan): Boolean = { + // We skip such case that Sort is after Limit since + // SparkStrategies will convert them to TakeOrderedAndProjectExec + val skipEliminate = child match { + case Sort(_, true, _) => true Review comment: I have the same feeling with @viirya now. It seems the performance depends on shuffle overheads (data size), so IMO its better to keep the current behaviour in this PR (so that we could control it, `TakeOrderedAndProjectExec or LIMIT+SORT`, by `topKSortFallbackThreshold`). ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org