Github user kayousterhout commented on a diff in the pull request: https://github.com/apache/spark/pull/12060#discussion_r60838822 --- Diff: core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala --- @@ -403,32 +403,47 @@ class DAGScheduler( parents.toList } - /** Find ancestor shuffle dependencies that are not registered in shuffleToMapStage yet */ - private def getAncestorShuffleDependencies(rdd: RDD[_]): Stack[ShuffleDependency[_, _, _]] = { - val parents = new Stack[ShuffleDependency[_, _, _]] + /** + * Find ancestor shuffle dependencies that are not registered in shuffleToMapStage yet. + * This is done in topological order to create ancestor stages first to ensure that the result + * stage graph is correctly built. + */ + private def getAncestorShuffleDependencies(rdd: RDD[_]): Seq[ShuffleDependency[_, _, _]] = { + val parents = new ArrayBuffer[ShuffleDependency[_, _, _]] val visited = new HashSet[RDD[_]] // We are manually maintaining a stack here to prevent StackOverflowError // caused by recursively visiting val waitingForVisit = new Stack[RDD[_]] def visit(r: RDD[_]) { - if (!visited(r)) { - visited += r - for (dep <- r.dependencies) { - dep match { - case shufDep: ShuffleDependency[_, _, _] => - if (!shuffleToMapStage.contains(shufDep.shuffleId)) { - parents.push(shufDep) - } - case _ => + if (visited(r)) { --- End diff -- Is the code change here fixing a correctness issue? Is this related to the performance issue described in the pull request?
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