otterc commented on a change in pull request #30691:
URL: https://github.com/apache/spark/pull/30691#discussion_r641257596
##########
File path: core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala
##########
@@ -2000,6 +2023,147 @@ private[spark] class DAGScheduler(
}
}
+ /**
+ * Schedules shuffle merge finalize.
+ */
+ private[scheduler] def scheduleShuffleMergeFinalize(stage: ShuffleMapStage):
Unit = {
+ logInfo(("%s (%s) scheduled for finalizing" +
+ " shuffle merge in %s s").format(stage, stage.name,
shuffleMergeFinalizeWaitSec))
+ shuffleMergeFinalizeScheduler.schedule(
+ new Runnable {
+ override def run(): Unit = finalizeShuffleMerge(stage)
+ },
+ shuffleMergeFinalizeWaitSec,
+ TimeUnit.SECONDS
+ )
+ }
+
+ /**
+ * DAGScheduler notifies all the remote shuffle services chosen to serve
shuffle merge request for
+ * the given shuffle map stage to finalize the shuffle merge process for
this shuffle. This is
+ * invoked in a separate thread to reduce the impact on the DAGScheduler
main thread, as the
+ * scheduler might need to talk to 1000s of shuffle services to finalize
shuffle merge.
+ */
+ private[scheduler] def finalizeShuffleMerge(stage: ShuffleMapStage): Unit = {
+ logInfo("%s (%s) finalizing the shuffle merge".format(stage, stage.name))
+ externalShuffleClient.foreach { shuffleClient =>
+ val shuffleId = stage.shuffleDep.shuffleId
+ val numMergers = stage.shuffleDep.getMergerLocs.length
+ val numResponses = new AtomicInteger()
+ val results = (0 until numMergers).map(_ =>
SettableFuture.create[Boolean]())
+ val timedOut = new AtomicBoolean()
+
+ def increaseAndCheckResponseCount(): Unit = {
+ if (numResponses.incrementAndGet() == numMergers) {
+ logInfo("%s (%s) shuffle merge finalized".format(stage, stage.name))
+ // Since this runs in the netty client thread and is outside of
DAGScheduler
+ // event loop, we only post ShuffleMergeFinalized event into the
event queue.
+ // The processing of this event should be done inside the event
loop, so it
+ // can safely modify scheduler's internal state.
+ eventProcessLoop.post(ShuffleMergeFinalized(stage))
+ }
+ }
+
+ stage.shuffleDep.getMergerLocs.zipWithIndex.foreach {
+ case (shuffleServiceLoc, index) =>
+ // Sends async request to shuffle service to finalize shuffle merge
on that host
+ // TODO: SPARK-35536: Cancel finalizeShuffleMerge if the stage is
cancelled
+ // TODO: during shuffleMergeFinalizeWaitSec
+ shuffleClient.finalizeShuffleMerge(shuffleServiceLoc.host,
+ shuffleServiceLoc.port, shuffleId,
+ new MergeFinalizerListener {
+ override def onShuffleMergeSuccess(statuses: MergeStatuses):
Unit = {
+ assert(shuffleId == statuses.shuffleId)
+ if (!timedOut.get()) {
+ eventProcessLoop.post(RegisterMergeStatuses(stage,
MergeStatus.
+ convertMergeStatusesToMergeStatusArr(statuses,
shuffleServiceLoc)))
+ increaseAndCheckResponseCount()
+ results(index).set(true)
+ }
+ }
+
+ override def onShuffleMergeFailure(e: Throwable): Unit = {
+ if (!timedOut.get()) {
+ logWarning(s"Exception encountered when trying to finalize
shuffle " +
+ s"merge on ${shuffleServiceLoc.host} for shuffle
$shuffleId", e)
+ increaseAndCheckResponseCount()
+ // Do not fail the future as this would cause dag scheduler
to prematurely
+ // give up on waiting for merge results from the remaining
shuffle services
+ // if one fails
+ results(index).set(false)
+ }
+ }
+ })
+ }
+ // DAGScheduler only waits for a limited amount of time for the merge
results.
+ // It will attempt to submit the next stage(s) irrespective of whether
merge results
+ // from all shuffle services are received or not.
+ // TODO: SPARK-33701: Instead of waiting for a constant amount of time
for finalization
+ // TODO: for all the stages, adaptively tune timeout for merge
finalization
+ try {
+ Futures.allAsList(results: _*).get(shuffleMergeResultsTimeoutSec,
TimeUnit.SECONDS)
+ } catch {
+ case _: TimeoutException =>
+ logInfo(s"Timed out on waiting for merge results from all " +
+ s"$numMergers mergers for shuffle $shuffleId")
+ timedOut.set(true)
+ eventProcessLoop.post(ShuffleMergeFinalized(stage))
+ }
+ }
+ }
+
+ private def processShuffleMapStageCompletion(shuffleStage: ShuffleMapStage):
Unit = {
+ markStageAsFinished(shuffleStage)
+ logInfo("looking for newly runnable stages")
+ logInfo("running: " + runningStages)
+ logInfo("waiting: " + waitingStages)
+ logInfo("failed: " + failedStages)
+
+ // This call to increment the epoch may not be strictly necessary, but it
is retained
+ // for now in order to minimize the changes in behavior from an earlier
version of the
+ // code. This existing behavior of always incrementing the epoch following
any
+ // successful shuffle map stage completion may have benefits by causing
unneeded
+ // cached map outputs to be cleaned up earlier on executors. In the future
we can
+ // consider removing this call, but this will require some extra
investigation.
+ // See https://github.com/apache/spark/pull/17955/files#r117385673 for
more details.
+ mapOutputTracker.incrementEpoch()
+
+ clearCacheLocs()
+
+ if (!shuffleStage.isAvailable) {
+ // Some tasks had failed; let's resubmit this shuffleStage.
+ // TODO: Lower-level scheduler should also deal with this
+ logInfo("Resubmitting " + shuffleStage + " (" + shuffleStage.name +
+ ") because some of its tasks had failed: " +
+ shuffleStage.findMissingPartitions().mkString(", "))
+ submitStage(shuffleStage)
+ } else {
+ markMapStageJobsAsFinished(shuffleStage)
+ submitWaitingChildStages(shuffleStage)
+ }
+ }
+
+ private[scheduler] def handleRegisterMergeStatuses(
+ stage: ShuffleMapStage,
+ mergeStatuses: Seq[(Int, MergeStatus)]): Unit = {
+ // Register merge statuses if the stage is still running and shuffle merge
is not finalized yet.
+ if (runningStages.contains(stage) &&
!stage.shuffleDep.shuffleMergeFinalized) {
+ mapOutputTracker.registerMergeResults(stage.shuffleDep.shuffleId,
mergeStatuses)
+ }
+ }
+
+ private[scheduler] def handleShuffleMergeFinalized(stage: ShuffleMapStage):
Unit = {
+ // Only update MapOutputTracker metadata if the stage is still active. i.e
not cancelled.
+ if (runningStages.contains(stage)) {
+ stage.shuffleDep.markShuffleMergeFinalized()
+ processShuffleMapStageCompletion(stage)
+ } else {
+ // TODO: SPARK-35549: Currently merge statuses results which come after
shuffle merge
+ // TODO: is finalized is not registered.
Review comment:
Just adding more clarification.
The below comment suggests that when the stage is cancelled then
finalizeShuffleMerge will be cancelled and with that there is no guarantee that
there is a ShuffleMergeFinalized event will be posted
```
// TODO: SPARK-35536: Cancel finalizeShuffleMerge if the stage is cancelled
// TODO: during shuffleMergeFinalizeWaitSec
```
So, unregistering of all the merge results should ideally happen when the
stage is cancelled.
Since that will be handled with another jira, I think it is better to handle
the unregisteration of all merge results with that jira as well.
In case you still want to keep it here, then please add a comment saying
something like: this is targeting a stage cancellation while the merge
finalization is not completed. Also, add the explanation that how it will
interfere with the new stage after cancellation and the TODO should point to
`SPARK-35536` where we will reconsider if we need to unregister here.
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