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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8163) Improve ActiveStandbyElector to provide hooks for fencing old active
Date Tue, 20 Mar 2012 18:09:39 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13233638#comment-13233638
] 

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

Hi Hari. I like your ideas about using this info znode for failover/restart preferences. But
I don't think it's a requirement for a first draft, and it's not clear what you mean by 'state
equalization' in your second point. We don't currently use this terminology.

Are you OK with the current design for a first draft? We can add improvements later -- I'm
using a protobuf for the info in ZK so we can evolve the information contained within without
breaking compatibility.
                
> 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: 0.24.0, 0.23.3
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: 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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