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https://issues.apache.org/jira/browse/HDFS-2983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13250943#comment-13250943
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Konstantin Shvachko commented on HDFS-2983:
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The scenario is not different if you do rolling or non-rolling upgrades. The
difference is that the patch *removes build version verification*, which means
that after 3 upgrades (rolling or not) you are guaranteed to have 3 sets of
nodes running different version of hadoop talking to your NameNode.
While in today's world the strict version verification guarantees that
un-upgraded nodes never talk to NN. If you add to this snapshots, block pools,
HA NameNodes it becomes an operability horror.
Separating snapshots from upgrades straightens things up, imho.
Todd, your proposal to add DN versions to the Web UI is also very important.
Otherwise it is hard to monitor cluster consistency.
> Relax the build version check to permit rolling upgrades within a release
> -------------------------------------------------------------------------
>
> Key: HDFS-2983
> URL: https://issues.apache.org/jira/browse/HDFS-2983
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.0.0
> Reporter: Eli Collins
> Assignee: Aaron T. Myers
> Attachments: HDFS-2983.patch, HDFS-2983.patch, HDFS-2983.patch,
> HDFS-2983.patch, HDFS-2983.patch, HDFS-2983.patch, HDFS-2983.patch
>
>
> Currently the version check for DN/NN communication is strict (it checks the
> exact svn revision or git hash, Storage#getBuildVersion calls
> VersionInfo#getRevision), which prevents rolling upgrades across any
> releases. Once we have the PB-base RPC in place (coming soon to branch-23)
> we'll have the necessary pieces in place to loosen this restriction, though
> perhaps it takes another 23 minor release or so before we're ready to commit
> to making the minor versions compatible.
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