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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7121) For JournalNode operations that must succeed on all nodes, attempt to undo the operation on all nodes if it fails on one node.
Date Fri, 10 Oct 2014 21:32:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14167553#comment-14167553
] 

Chris Nauroth commented on HDFS-7121:
-------------------------------------

I agree that a pre-check strategy is likely to be good enough.  Upgrade and rollback are operations
that execute infrequently.  Typically they're done during periods of low activity on the cluster
with a close watch by an admin.  Clients can't really connect anyway.  It's highly likely
that a pre-check would expose potential problems in most realistic scenarios, and the inherent
time-of-check/time-of-use race condition is unlikely to happen.  I'm going to draft a prototype
patch for a pre-check RPC.

> For JournalNode operations that must succeed on all nodes, attempt to undo the operation
on all nodes if it fails on one node.
> ------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-7121
>                 URL: https://issues.apache.org/jira/browse/HDFS-7121
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: journal-node
>            Reporter: Chris Nauroth
>
> Several JournalNode operations are not satisfied by a quorum.  They must succeed on every
JournalNode in the cluster.  If the operation succeeds on some nodes, but fails on others,
then this may leave the nodes in an inconsistent state and require operations to do manual
recovery steps.  For example, if {{doPreUpgrade}} succeeds on 2 nodes and fails on 1 node,
then the operator will need to correct the problem on the failed node and also manually restore
the previous.tmp directory to current on the 2 successful nodes before reattempting the upgrade.



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