Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/11210#discussion_r53534757
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
---
@@ -316,6 +316,21 @@ abstract class UnaryNode extends LogicalPlan {
override def children: Seq[LogicalPlan] = child :: Nil
override protected def validConstraints: Set[Expression] =
child.constraints
+
+ override def statistics: Statistics = {
+ // There should be some overhead in Row object, the size should not be
zero when there is
+ // no columns, this help to prevent divide-by-zero error.
+ val childRowSize = child.output.map(_.dataType.defaultSize).sum + 8
+ val outputRowSize = output.map(_.dataType.defaultSize).sum + 8
+ // Assume there will be the same number of rows as child has.
+ var sizeInBytes = (child.statistics.sizeInBytes * outputRowSize) /
childRowSize
--- End diff --
I see, e.g. if the input is `Long` but output is `Int` then our size should
be half our child's. I think it would be slightly clearer if this read
```
child.statistics.sizeInBytes * (outputRowSize / childRowSize)
```
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