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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2949) HA: Add check to active state transition to prevent operator-induced split brain
Date Thu, 15 Mar 2012 21:12:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2949?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13230550#comment-13230550

Todd Lipcon commented on HDFS-2949:

Another safety check here is to make sure that the transaction IDs match between the nodes
before going active.
> HA: Add check to active state transition to prevent operator-induced split brain
> --------------------------------------------------------------------------------
>                 Key: HDFS-2949
>                 URL: https://issues.apache.org/jira/browse/HDFS-2949
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: ha, name-node
>    Affects Versions: 0.24.0
>            Reporter: Todd Lipcon
> Currently, if the administrator mistakenly calls "-transitionToActive" on one NN while
the other one is still active, all hell will break loose. We can add a simple check by having
the NN make a getServiceState() RPC to its peer with a short (~1 second?) timeout. If the
RPC succeeds and indicates the other node is active, it should refuse to enter active mode.
If the RPC fails or indicates standby, it can proceed.
> This is just meant as a preventative safety check - we still expect users to use the
"-failover" command which has other checks plus fencing built in.

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