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https://issues.apache.org/jira/browse/HDFS-3561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13402978#comment-13402978
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Vinay commented on HDFS-3561:
-----------------------------
{quote}This isn't acceptable. The point of fencing is to ensure that if the
previously-active NN returns from appearing to have been down, it doesn't start
writing to the shared directory again while the new active is also writing to
that directory.{quote}
If the shared storage provides good fencing, so that if it is fenced once and
not allowing to write anymore from old writer then this situation will never
come.
If the fail-over not happening due to fencing failure of old active that means
network down is not supported in ZKFC..?
I think, taking transitioning current standby to Active in the current
situation will be the correct behavior.
Any thoughts on this..?
> ZKFC retries for 45 times to connect to other NN during fencing when network
> between NNs broken and standby Nn will not take over as active
> --------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-3561
> URL: https://issues.apache.org/jira/browse/HDFS-3561
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: auto-failover
> Reporter: suja s
> Assignee: Vinay
>
> Scenario:
> Active NN on machine1
> Standby NN on machine2
> Machine1 is isolated from the network (machine1 network cable unplugged)
> After zk session timeout ZKFC at machine2 side gets notification that NN1 is
> not there.
> ZKFC tries to failover NN2 as active.
> As part of this during fencing it tries to connect to machine1 and kill NN1.
> (sshfence technique configured)
> This connection retry happens for 45 times( as it takes
> ipc.client.connect.max.socket.retries)
> Also after that standby NN is not able to take over as active (because of
> fencing failure).
> Suggestion: If ZKFC is not able to reach other NN for specified time/no of
> retries it can consider that NN as dead and instruct the other NN to take
> over as active as there is no chance of the other NN (NN1) retaining its
> state as active after zk session timeout when its isolated from network
> From ZKFC log:
> {noformat}
> 2012-06-21 17:46:14,378 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 22 time(s).
> 2012-06-21 17:46:35,378 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 23 time(s).
> 2012-06-21 17:46:56,378 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 24 time(s).
> 2012-06-21 17:47:17,378 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 25 time(s).
> 2012-06-21 17:47:38,382 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 26 time(s).
> 2012-06-21 17:47:59,382 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 27 time(s).
> 2012-06-21 17:48:20,386 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 28 time(s).
> 2012-06-21 17:48:41,386 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 29 time(s).
> 2012-06-21 17:49:02,386 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 30 time(s).
> 2012-06-21 17:49:23,386 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 31 time(s).
> {noformat}
>
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