beliefer commented on a change in pull request #27429: [SPARK-28330][SQL]
Support ANSI SQL: result offset clause in query expression
URL: https://github.com/apache/spark/pull/27429#discussion_r383677027
##########
File path: sql/core/src/main/scala/org/apache/spark/sql/execution/limit.scala
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@@ -161,6 +164,46 @@ case class GlobalLimitExec(limit: Int, child: SparkPlan)
extends BaseLimitExec {
override def outputOrdering: Seq[SortOrder] = child.outputOrdering
}
+/**
+ * Skip the first `offset` elements then take the first `limit` of the
following elements in
+ * the child's single output partition.
+ */
+case class GlobalLimitAndOffsetExec(
+ limit: Int,
+ offset: Int,
+ child: SparkPlan) extends BaseLimitExec {
+
+ override def requiredChildDistribution: List[Distribution] = AllTuples :: Nil
+
+ override def outputPartitioning: Partitioning = child.outputPartitioning
+
+ override def outputOrdering: Seq[SortOrder] = child.outputOrdering
+
+ override def doExecute(): RDD[InternalRow] = {
+ val rdd = child.execute().mapPartitions { iter => iter.take(limit +
offset)}
+ val skips = rdd.take(offset)
Review comment:
Yes, but if the limit was a huge number, it still will throw OOM.
This PR only follows the implement of `BaseLimitExec`
https://github.com/apache/spark/blob/14ca8d326fcc5035da5b7a99772aacff8edad163/sql/core/src/main/scala/org/apache/spark/sql/execution/limit.scala#L109
If this is an issue, `GlobalLimitExec` and `LocalLimitExec` need to resolve
too.
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