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From "Uma Maheswara Rao G (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3561) 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
Date Mon, 02 Jul 2012 18:33:43 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13405222#comment-13405222
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Uma Maheswara Rao G commented on HDFS-3561:
-------------------------------------------

Hi Aaron, Thanks a lot.

{code}
    for example if we have shared storage fencing at writer level. Whenever new writer comes,
automatically old writer will not be allowed.

I'm not sure what you mean by this.
{code}
What I mean by this is, take a case of BookKeeper:
BookKeeper itself has a fencing logic. Whenever we open a new ledger, automatically it will
get fenced. Other clients will not be able to proceed for further writes.
I hope similar logic may come in QJM also using some writer level epoch numbers.

May be we need to develop a fence method with this clients and fence the things, but only
the thing i don't like is I need to to place that client libraries in ZKFC(this step may not
be required as NN's respective JM's will any way has to open writer, that writer itself will
fence automatically). I hope u understand my point here.


  

                
> 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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