Github user markhamstra commented on a diff in the pull request:
https://github.com/apache/spark/pull/11720#discussion_r57605206
--- Diff: core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala
---
@@ -286,6 +286,7 @@ class DAGScheduler(
case None =>
// We are going to register ancestor shuffle dependencies
getAncestorShuffleDependencies(shuffleDep.rdd).foreach { dep =>
+ assert(!shuffleToMapStage.get(dep.shuffleId).isDefined)
--- End diff --
Overwriting entries in `shuffleToMapStage` definitely isn't an outright
error -- we should still get correct results after the overwrite; so we
shouldn't be adding this new assertion to change an evaluation path that was
generating correct results into an error condition.
There are other open efforts to clean up this creation of additional Stages
that will be skipped instead of just re-using the prior-executed Stage more
cleanly. That issue is orthogonal to the generation of a topological ordering
of the dependencies, so I'd prefer to handle it outside of this PR.
cc @squito
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