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https://issues.apache.org/jira/browse/YARN-10295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17126577#comment-17126577
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Szilard Nemeth commented on YARN-10295:
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Hi [~bteke],
Looked at patch [^YARN-10295.001.branch-3.2.patch].
Can you please add an explanation comment and a jira reference as welll
(YARN-10295) in order to keep this variable as is, above the if block?
Just by seeing a variable (reservedContainer) that is used in two places right
below it's declaration, someone would have triggered to refactor, inlining the
variable and we are back to square one and people won't notice it was a bad
move because it seems an innocent touch.
> CapacityScheduler NPE can cause apps to get stuck without resources
> -------------------------------------------------------------------
>
> Key: YARN-10295
> URL: https://issues.apache.org/jira/browse/YARN-10295
> Project: Hadoop YARN
> Issue Type: Bug
> Components: capacityscheduler
> Affects Versions: 3.1.0, 3.2.0
> Reporter: Benjamin Teke
> Assignee: Benjamin Teke
> Priority: Major
> Attachments: YARN-10295.001.branch-3.1.patch,
> YARN-10295.001.branch-3.2.patch
>
>
> When the CapacityScheduler Asynchronous scheduling is enabled and log level
> is set to DEBUG there is an edge-case where a NullPointerException can cause
> the scheduler thread to exit and the apps to get stuck without allocated
> resources. Consider the following log:
> {code:java}
> 2020-05-27 10:13:49,106 INFO fica.FiCaSchedulerApp
> (FiCaSchedulerApp.java:apply(681)) - Reserved
> container=container_e10_1590502305306_0660_01_000115, on node=host:
> ctr-e148-1588963324989-31443-01-000002.hwx.site:25454 #containers=14
> available=<memory:2048, vCores:11> used=<memory:182272, vCores:14> with
> resource=<memory:4096, vCores:1>
> 2020-05-27 10:13:49,134 INFO fica.FiCaSchedulerApp
> (FiCaSchedulerApp.java:internalUnreserve(743)) - Application
> application_1590502305306_0660 unreserved on node host:
> ctr-e148-1588963324989-31443-01-000002.hwx.site:25454 #containers=14
> available=<memory:2048, vCores:11> used=<memory:182272, vCores:14>, currently
> has 0 at priority 11; currentReservation <memory:0, vCores:0> on node-label=
> 2020-05-27 10:13:49,134 INFO capacity.CapacityScheduler
> (CapacityScheduler.java:tryCommit(3042)) - Allocation proposal accepted
> 2020-05-27 10:13:49,163 ERROR yarn.YarnUncaughtExceptionHandler
> (YarnUncaughtExceptionHandler.java:uncaughtException(68)) - Thread
> Thread[Thread-4953,5,main] threw an Exception.
> java.lang.NullPointerException
> at
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler.allocateContainerOnSingleNode(CapacityScheduler.java:1580)
> at
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler.allocateContainersToNode(CapacityScheduler.java:1767)
> at
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler.allocateContainersToNode(CapacityScheduler.java:1505)
> at
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler.schedule(CapacityScheduler.java:546)
> at
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler$AsyncScheduleThread.run(CapacityScheduler.java:593)
> {code}
> A container gets allocated on a host, but the host doesn't have enough
> memory, so after a short while it gets unreserved. However because the
> scheduler thread is running asynchronously it might have entered into the
> following if block located in
> [CapacityScheduler.java#L1602|https://github.com/apache/hadoop/blob/7136ebbb7aa197717619c23a841d28f1c46ad40b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/CapacityScheduler.java#L1602],
> because at the time _node.getReservedContainer()_ wasn't null. Calling it a
> second time for getting the ApplicationAttemptId would be an NPE, as the
> container got unreserved in the meantime.
> {code:java}
> // Do not schedule if there are any reservations to fulfill on the node
> if (node.getReservedContainer() != null) {
> if (LOG.isDebugEnabled()) {
> LOG.debug("Skipping scheduling since node " + node.getNodeID()
> + " is reserved by application " + node.getReservedContainer()
> .getContainerId().getApplicationAttemptId());
> }
> return null;
> }
> {code}
> A fix would be to store the container object before the if block.
> Only branch-3.1/3.2 is affected, because the newer branches have YARN-9664
> which indirectly fixed this.
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