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From "Daniel Templeton (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-5677) RM can be in active-active state for an extended period
Date Wed, 28 Sep 2016 16:21:20 GMT

    [ https://issues.apache.org/jira/browse/YARN-5677?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15530124#comment-15530124

Daniel Templeton commented on YARN-5677:

[~jianhe], is leader election on by default in Hadoop 3?  I'd recommend it.  Shall I roll
that into the patch for this JIRA?

> RM can be in active-active state for an extended period
> -------------------------------------------------------
>                 Key: YARN-5677
>                 URL: https://issues.apache.org/jira/browse/YARN-5677
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: resourcemanager
>    Affects Versions: 2.7.3, 3.0.0-alpha1
>            Reporter: Daniel Templeton
>            Assignee: Daniel Templeton
>            Priority: Critical
> Both branch-2.8/trunk and branch-2.7 have issues when the active RM loses contact with
the ZK node(s).
> In branch-2.7, the RM will retry the connection 1000 times by default.  Attempting to
contact a node which cannot be reached is slow, which means the active can take over an hour
to realize it is no longer active.  I clocked it at about an hour and a half in my tests.
 The solution appears to be to add some time awareness into the retry loop.
> In branch-2.8/trunk, there is no maximum number of retries that I see.  It appears the
connection will be retried forever, with the active never figuring out it's no longer active.
 In my testing, the active-active state lasted almost 2 hours with no sign of stopping before
I killed it.  The solution appears to be to cap the number of retries or amount of time spent
> This issue is significant because of the asynchronous nature of job submission.  If the
active doesn't know it's not active, it will buffer up job submissions until it finally realizes
it has become the standby. Then it will fail all the job submissions in bulk. In high-volume
workflows, that behavior can create huge mass job failures.
> This issue is also important because the node managers will not fail over to the new
active until the old active realizes it's the standby.  Workloads submitted after the old
active loses contact with ZK will therefore fail to be executed regardless of which RM the
clients contact.

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