Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/1238#discussion_r15020066
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
---
@@ -26,6 +26,28 @@ import org.apache.spark.sql.catalyst.trees
abstract class LogicalPlan extends QueryPlan[LogicalPlan] {
self: Product =>
+ // TODO: handle overflow?
+ /**
+ * Estimates of various statistics. The default estimation logic simply
sums up the corresponding
+ * statistic produced by the children. To override this behavior,
override `statistics` and
+ * assign it a overriden version of `Statistics`.
+ */
+ case class Statistics(
+ /**
+ * Number of output tuples. For leaf operators this defaults to 1,
otherwise it is set to the
+ * product of children's `numTuples`.
+ */
+ numTuples: Long = childrenStats.map(_.numTuples).product,
+
+ /**
+ * Physical size in bytes. For leaf operators this defaults to 1,
otherwise it is set to the
+ * product of children's `sizeInBytes`.
+ */
+ sizeInBytes: Long = childrenStats.map(_.sizeInBytes).product
+ )
+ lazy val statistics: Statistics = new Statistics
+ lazy val childrenStats = children.map(_.statistics)
--- End diff --
I was suggesting we turn it into a def, remove it entirely, or stop
memoizing statistics. Double memoization seems unnecessarily expensive memory
wise.
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