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https://issues.apache.org/jira/browse/HADOOP-10251?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13973090#comment-13973090
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Uma Maheswara Rao G commented on HADOOP-10251:
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I think your idea will work and patch almost looks good to me.
One question:
{code}
/**
+ * Callback interface for service state change events.
+ *
+ * This interface is called whenever there is a change in the service state.
+ */
{code}
Seems like this interface will be called on every health monitor status check.
But doc says its a service state changed event. It is exposing impl details as
you do that state comparisions in implementation and do necessary actions on
state change. So, at this interface level, we are not sure whether service
state changed from last state or not right. Can you update this something like
Service state notification?
> Both NameNodes could be in STANDBY State if SNN network is unstable
> -------------------------------------------------------------------
>
> Key: HADOOP-10251
> URL: https://issues.apache.org/jira/browse/HADOOP-10251
> Project: Hadoop Common
> Issue Type: Bug
> Components: ha
> Affects Versions: 2.2.0
> Reporter: Vinayakumar B
> Assignee: Vinayakumar B
> Priority: Critical
> Attachments: HADOOP-10251.patch, HADOOP-10251.patch,
> HADOOP-10251.patch, HADOOP-10251.patch
>
>
> Following corner scenario happened in one of our cluster.
> 1. NN1 was Active and NN2 was Standby
> 2. NN2 machine's network was slow
> 3. NN1 got shutdown.
> 4. NN2 ZKFC got the notification and trying to check for old active for
> fencing. (This took little more time, again due to slow network)
> 5. In between, NN1 got restarted by our automatic monitoring, and ZKFC made
> it Active.
> 6. Now NN2 ZKFC got Old Active as NN1 and it did graceful fencing of NN1 to
> STANBY.
> 7. Before writing ActiveBreadCrumb to ZK, NN2 ZKFC got session timeout and
> got shutdown before making NN2 Active.
> *Now cluster having both NameNodes as STANDBY.*
> NN1 ZKFC still thinks that its nameNode is in Active state.
> NN2 ZKFC waiting for election.
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