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From "Aaron T. Myers (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, 25 Jun 2012 19:57:44 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13400833#comment-13400833
] 

Aaron T. Myers commented on HDFS-3561:
--------------------------------------

bq. 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

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.

bq. I think we can set retries to 1/2 for avoiding unnecessary actions on small nw fluctuations?
or we can set it to 0 as we are already setting the same values in ConfiguredFailoverProxyProvider
for failover clients.

We set it to 0 in ConfiguredFailoverProxyProvider because we want to trying failing over immediately
as the retry mechanism, instead of repeatedly trying to contact a machine that may in fact
be completely down.

I agree, though, that setting it to a lower number than 45 makes sense in the case of the
client in the ZKFC, and perhaps making it configurable separately.
                
> 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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