Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/469#discussion_r11877333
--- Diff: core/src/main/scala/org/apache/spark/rdd/RDD.scala ---
@@ -236,6 +236,21 @@ abstract class RDD[T: ClassTag](
}
/**
+ * Return the ancestors of the given RDD that are related to it only
through a sequence of
+ * narrow dependencies. This traverses the given RDD's dependency tree
using DFS.
+ */
+ private[spark] def getNarrowAncestors(
+ ancestors: ArrayBuffer[RDD[_]] = ArrayBuffer.empty): Seq[RDD[_]] = {
+ val narrowDependencies = dependencies.collect { case d:
NarrowDependency[_] => d }
+ val narrowParents = narrowDependencies.map(_.rdd)
+ narrowParents.foreach { parent =>
+ ancestors += parent
--- End diff --
`rdd.union(rdd)` actually does not produce a cycle. The resulting tree has
a root `UnionRDD` and two identical children `rdd`.
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