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From "Sanjay Radia (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2983) Relax the build version check to permit rolling upgrades within a release
Date Fri, 06 Apr 2012 20:17:24 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13248693#comment-13248693
] 

Sanjay Radia commented on HDFS-2983:
------------------------------------

Upgrades involves snapshots on NN and DNs. Snapshots are not just for layout changes but also
for data protection against a version change that introduced a bug that has the potential
to wipe out a portion of the data. (other systems ask the admin to do a backup before starting
the upgrade - that does not make sense for HDFS).
HDFS's snapshot feature is a unique and powerful part of HDFS's upgrade. 

Yahoo does snapshot as part of all upgrades, except for  EBFs that do not touching the core
of the file system.
At this stage I don't know what snapshots mean for rolling upgrades.
This requires further thought.
                
> 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
>
>
> 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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