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https://issues.apache.org/jira/browse/HDFS-2983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13250366#comment-13250366
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Todd Lipcon commented on HDFS-2983:
-----------------------------------

bq. The scenario that scares me is if somebody does a snapshot, then several 
rolling upgrades, and then decides to rollback. This may be possible, but seems 
to be very much error-prone.

Why is this scenario different than if somebody does a snapshot, then several 
_non-rolling_ upgrades, then decides to rollback? In both cases, we have the 
case of a newer version trying to do a rollback to an older version snapshot. 
Right?
                
> 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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