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https://issues.apache.org/jira/browse/HDFS-11094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15716729#comment-15716729
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Eric Badger commented on HDFS-11094:
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bq. I think the existing tests are quite adequate. I understand that a
full-blown mini cluster is sometimes needed to test the distributed file
system. However, we should avoid adding such end-to-end tests if it is possible
to have reasonable unit tests.
Upon looking at this again, I agree with [~kihwal]. I don't think that it is
necessary for us to use a minicluster in this case. The current tests are
adequate IMO since they test the methods that are directly used on either side
of the version request. Additionally, the minicluster is expensive and creating
a unit test with the minicluster would be difficult in this case since it
requires a heartbeat to get out of its build() method (though difficulty is not
my main objection).
> Send back HAState along with NamespaceInfo during a versionRequest as an
> optional parameter
> -------------------------------------------------------------------------------------------
>
> Key: HDFS-11094
> URL: https://issues.apache.org/jira/browse/HDFS-11094
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Eric Badger
> Assignee: Eric Badger
> Attachments: HDFS-11094.001.patch, HDFS-11094.002.patch,
> HDFS-11094.003.patch, HDFS-11094.004.patch, HDFS-11094.005.patch,
> HDFS-11094.006.patch, HDFS-11094.007.patch, HDFS-11094.008.patch,
> HDFS-11094.009.patch
>
>
> The datanode should know which NN is active when it is connecting/registering
> to the NN. Currently, it only figures this out during its first (and
> subsequent) heartbeat(s) and so there is a period of time where the datanode
> is alive and registered, but can't actually do anything because it doesn't
> know which NN is active. A byproduct of this is that the MiniDFSCluster will
> become active before it knows what NN is active, which can lead to NPEs when
> calling getActiveNN().
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