Github user mateiz commented on a diff in the pull request:
https://github.com/apache/incubator-spark/pull/641#discussion_r10003953
--- Diff: core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala
---
@@ -272,8 +272,10 @@ class DAGScheduler(
if (mapOutputTracker.has(shuffleDep.shuffleId)) {
val serLocs =
mapOutputTracker.getSerializedMapOutputStatuses(shuffleDep.shuffleId)
val locs = MapOutputTracker.deserializeMapStatuses(serLocs)
- for (i <- 0 until locs.size) stage.outputLocs(i) = List(locs(i))
- stage.numAvailableOutputs = locs.size
+ for (i <- 0 until locs.size) {
+ stage.outputLocs(i) = Option(locs(i)).toList // locs(i) will be
null if missing
--- End diff --
Yeah, the problem is that the MapOutputTracker returns an array of
MapStatus, where position i of the array is supposed to be the location of the
output of task i. This array contains nulls initially to denote a missing
location, because a MapStatus can only indicate a real location. So I think
that either way we'll have to check for some "missing output" condition.
With this fix I believe we won't be launching reduce stages when some maps
are missing anymore, so we should be okay.
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