Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/16696#discussion_r104546713
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala
---
@@ -773,14 +773,20 @@ case class LocalLimit(limitExpr: Expression, child:
LogicalPlan) extends UnaryNo
}
override def computeStats(conf: CatalystConf): Statistics = {
val limit = limitExpr.eval().asInstanceOf[Int]
- val sizeInBytes = if (limit == 0) {
+ val childStats = child.stats(conf)
+ if (limit == 0) {
// sizeInBytes can't be zero, or sizeInBytes of BinaryNode will also
be zero
// (product of children).
- 1
+ Statistics(
+ sizeInBytes = 1,
+ rowCount = Some(0),
+ isBroadcastable = childStats.isBroadcastable)
} else {
- (limit: Long) * output.map(a => a.dataType.defaultSize).sum
+ // The output row count of LocalLimit should be the sum of row count
from each partition, but
+ // since the partition number is not available here, we just use
statistics of the child
+ // except column stats, because we don't know the distribution after
a limit operation
--- End diff --
Nit: the whole sentence does not have a period. How about rewriting it like?
> The output row count of LocalLimit should be the sum of row counts from
each partition. However, since the number of partitions is not available here,
we just use statistics of the child. Because the distirubtion after a limit
operation is unknown, we do not propapage the column stats.
---
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