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https://issues.apache.org/jira/browse/HADOOP-8163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13233655#comment-13233655
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Hari Mankude commented on HADOOP-8163:
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Design looks good. We can decide on whether info znode cleanup for a clean
shutdown is required or not later on. By state equalization, I meant that in a
situation where there is no shared storage, (something like journal daemon),
there might be situations where standby might not be able take over since it
does not have access to the entire set of latest editlogs. If this is a
switchover situation, then these editlogs can be pulled over from the active.
If active NN is dead, then standby cannot become active without loss of data.
Using quorum on journals (with stopping of the NN service with loss of quorum)
is another approach.
info znode is very useful in solving some basic HA issues for automatic
failover.
patch looks good.
> 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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