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https://issues.apache.org/jira/browse/HDFS-4463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13568938#comment-13568938
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Colin Patrick McCabe commented on HDFS-4463:
--------------------------------------------
moving to HDFS, since it's about ZKFC.
> ActiveStandbyElector can join election even before Service HEALTHY, and
> results in null data at ActiveBreadCrumb
> ----------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-4463
> URL: https://issues.apache.org/jira/browse/HDFS-4463
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: ha
> Affects Versions: 2.0.2-alpha
> Reporter: Vinay
> Assignee: Vinay
> Priority: Critical
>
> ActiveStandbyElector can store null at ActiveBreadCrumb in the below race
> condition. At further all failovers will fail resulting NPE.
> 1. ZKFC restarted.
> 2. due to less machine busy, first zk connection is expired even before the
> health monitoring returned the status.
> 3. On re-establishment transitionToActive will be called, at this time
> appData will be null,
> 4. So now ActiveBreadCrumb will have null.
> 5. After this any failovers will fail throwing
> {noformat}java.lang.NullPointerException
> at
> org.apache.hadoop.util.StringUtils.byteToHexString(StringUtils.java:171)
> at
> org.apache.hadoop.ha.ActiveStandbyElector.fenceOldActive(ActiveStandbyElector.java:892)
> at
> org.apache.hadoop.ha.ActiveStandbyElector.becomeActive(ActiveStandbyElector.java:797)
> at
> org.apache.hadoop.ha.ActiveStandbyElector.processResult(ActiveStandbyElector.java:475)
> at
> org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:545)
> at
> org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:497){noformat}
> Should not join the election before service is HEALTHY
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