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https://issues.apache.org/jira/browse/HDFS-3192?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13246852#comment-13246852
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Hari Mankude commented on HDFS-3192:
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bq.Can you explain why it has to restart, instead of just transitioning to
standby? What do you mean by "in limbo" here?
"in limbo" implies that NN1 thinks that it is active even though NN2 has taken
over since it has not tried to access editlogs. So, it is not behaving as
standby and keeping up with active. Are you suggesting that ZKFC1 does
transitionToStandby() when it loses znode? On an active NN, there is a high
probability that it might abort. Also, does transitionToStandby() guarantee
that all the active-state threads have quisced?
bq.Before issuing an "uncontrolled abort", the ZKFC2 will always try to do a
"graceful fence" – ie ask it to self-resign via an RPC. See the
tryGracefulFence function in the FailoverController class.
I don't think that doing tryGraceFulFence() from NN2 to NN1 is safe. First of
all, this is opening up one more channel of communication between NN1 and NN2
and this is subject to various races sequences, split-brain etc. I think
self-resign is much safer than trygracefulfence(). So far, I dont see a lack of
correctness argument in our discussion. Is my description correct here?
> Active NN should exit when it has not received a getServiceStatus() rpc from
> ZKFC for timeout secs
> --------------------------------------------------------------------------------------------------
>
> Key: HDFS-3192
> URL: https://issues.apache.org/jira/browse/HDFS-3192
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ha, name-node
> Reporter: Hari Mankude
> Assignee: Hari Mankude
>
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