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From "Aaron T. Myers (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8163) Improve ActiveStandbyElector to provide hooks for fencing old active
Date Thu, 22 Mar 2012 00:23:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13235247#comment-13235247
] 

Aaron T. Myers commented on HADOOP-8163:
----------------------------------------

Thanks for addressing my comments, Todd. I think this patch looks a lot better. IllegalStateException
is a good choice instead of AssertionError.

A few nits follow. +1 once these are addressed:

# 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.
# Maybe include the path of the ZNode in the log message "Writing record of this node as the
most recent active..."
# We're now using CamelCase for all ZNode names, but two comments still reference a dash-separated
name.
# I still think we should rename operationSuccess, etc. Feel free to punt to another JIRA.
                
> 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, 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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