Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/3531#discussion_r21129941
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala ---
@@ -148,20 +148,15 @@ case class Limit(limit: Int, child: SparkPlan)
}
override def execute() = {
- val rdd: RDD[_ <: Product2[Boolean, Row]] = if (sortBasedShuffleOn) {
- child.execute().mapPartitions { iter =>
- iter.take(limit).map(row => (false, row.copy()))
+ if (sortBasedShuffleOn) {
+ child.execute().map(_.copy).coalesce(1).mapPartitions { iter =>
+ iter.take(limit)
--- End diff --
You do need to `copy()` before any `take` or `collect` operation because
SparkSQL will reuse row objects and these operations create arrays that will
end up all containing the same object.
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