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Date: Thu, 22 Mar 2012 22:24:22 +0000 (UTC)
From: "Todd Lipcon (Commented) (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HADOOP-8163) Improve ActiveStandbyElector to
 provide hooks for fencing old active
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    [ https://issues.apache.org/jira/browse/HADOOP-8163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13236116#comment-13236116 ] 

Todd Lipcon commented on HADOOP-8163:
-------------------------------------

bq. Am I missing something, or are ensureBaseZNode and baseNodeExists only called by the tests? If so, we should probably relocate them, or at least mark them @VisibleForTesting if they can't be moved for some reason.
These are used by my forthcoming patch for the ZK-based automatic failover controller. The ZKFC has a "-formatZK" flag which calls through to ensureBaseZNode. Once this gets committed I'll move forward uploading the patch there.

I fixed the other three of ATM's comments. I'll wait til tomorrow to commit this in case Bikas has any additional feedback.
                
> Improve ActiveStandbyElector to provide hooks for fencing old active
> --------------------------------------------------------------------
>
>                 Key: HADOOP-8163
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8163
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: ha
>    Affects Versions: 0.23.3, 0.24.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hadoop-8163.txt, hadoop-8163.txt, hadoop-8163.txt
>
>
> When a new node becomes active in an HA setup, it may sometimes have to take fencing actions against the node that was formerly active. This JIRA extends the ActiveStandbyElector which adds an extra non-ephemeral node into the ZK directory, which acts as a second copy of the active node's information. Then, if the active loses its ZK session, the next active to be elected may easily locate the unfenced node to take the appropriate actions.

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