Github user markhamstra commented on a diff in the pull request:
https://github.com/apache/incubator-spark/pull/641#discussion_r9996859
--- 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 --
Ok, it was a bad assumption on my part that the mapOutputTracker would only
be returning valid locations, and this PR does address the possibility of null
values here. However, it feels to me like it is addressing the symptom instead
of the cause. Wouldn't we be better off either not putting nulls into the
MapOutputTracker in the first place, or at least not returning them when
getting map output statuses? As it stands, null checks are probably needed
everywhere the output statuses are fetched.
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