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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2179) HA: namenode fencing mechanism
Date Thu, 04 Aug 2011 16:49:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13079459#comment-13079459
] 

Aaron T. Myers commented on HDFS-2179:
--------------------------------------

Latest patch looks great. One tiny comment

In the loop in {{NodeFencer.fence}}, why do you continue in the event of {{BadFencingConfigurationException}},
but not in the case of an unknown {{Throwable}}? I can imagine a justification for continuing
in both or neither cases, but not in only one.

+1 once this is addressed.

> HA: namenode fencing mechanism
> ------------------------------
>
>                 Key: HDFS-2179
>                 URL: https://issues.apache.org/jira/browse/HDFS-2179
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-2179.txt, hdfs-2179.txt
>
>
> In an HA cluster, when there are two NNs, the invariant that only one NN is active at
a time has to be preserved in order to prevent "split brain syndrome." Thus, when a standby
NN is transition to "active" state during a failover, it needs to somehow _fence_ the formerly
active NN to ensure that it can no longer perform edits. This JIRA is to discuss and implement
NN fencing.

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