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https://issues.apache.org/jira/browse/HDFS-2983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13250001#comment-13250001
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Konstantin Shvachko commented on HDFS-2983:
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I'd like to reiterate on Sanjay's point. If you start rolling upgrade with
snapshot creation it can get very messy. Some nodes will be creating snapshots
with new version and some will continue with the old. Then rollback will become
tricky if possible at all. Two question in this regard:
# What is the procedure for rolling upgrade? I mean the exact sequence of steps
admins will follow to upgrade a cluster.
# Can we distinguish between rolling and old-style upgrades and never allow
them simultaneously. Feels like this should be the precondition for relaxing
the version matching condition.
> 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
>
>
> 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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