Github user mccheah commented on a diff in the pull request:
https://github.com/apache/spark/pull/8007#discussion_r37357691
--- Diff:
core/src/main/scala/org/apache/spark/scheduler/cluster/YarnSchedulerBackend.scala
---
@@ -91,6 +92,66 @@ private[spark] abstract class YarnSchedulerBackend(
}
/**
+ * Override the DriverEndpoint to add extra logic for the case when an
executor is disconnected.
+ * We should check the cluster manager and find if the loss of the
executor was caused by YARN
+ * force killing it due to preemption.
+ */
+ private class YarnDriverEndpoint(rpcEnv: RpcEnv, sparkProperties:
ArrayBuffer[(String, String)])
+ extends DriverEndpoint(rpcEnv, sparkProperties) {
+
+ private val pendingDisconnectedExecutors = new HashSet[String]
+ private val handleDisconnectedExecutorThreadPool =
+
ThreadUtils.newDaemonCachedThreadPool("yarn-driver-handle-lost-executor-thread-pool")
+
+ /**
+ * When onDisconnected is received at the driver endpoint, the
superclass DriverEndpoint
+ * handles it by assuming the Executor was lost for a bad reason and
removes the executor
+ * immediately.
+ *
+ * In YARN's case however it is crucial to talk to the application
master and ask why the
+ * executor had exited. In particular, the executor may have exited
due to the executor
+ * having been preempted. If the executor "exited normally" according
to the application
+ * master then we pass that information down to the TaskSetManager to
inform the
+ * TaskSetManager that tasks on that lost executor should not count
towards a job failure.
+ */
+ override def onDisconnected(rpcAddress: RpcAddress): Unit = {
--- End diff --
I guess there will be wasted work in the sense that the tasks will get
allocated to the bad executor and then the executor will be removed and all of
those tasks are relocated to the healthy ones. That's probably fine from a
correctness standpoint but might create a bit of a performance latency... I'm
open to the discussion of doing another architecture overhaul to get the
soft-unregistration construct done.
The other thing I'm wondering is if it's even worth offloading this
communicate-with-AM logic to be asynchronous at all. How big of a performance
penalty would it be to block the event loop with the request to the AM for the
get-executor-loss-reason? I presumed that it was unacceptable to do that
blocking request on the main event loop though.
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