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From "Sean Mackrory (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11096) Support rolling upgrade between 2.x and 3.x
Date Thu, 05 Jan 2017 20:03:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15802380#comment-15802380
] 

Sean Mackrory commented on HDFS-11096:
--------------------------------------

In the SortedMapWritable case, the class is actually still there in the same package, but
it's now templated slightly differently to avoid a warning. This actually did cause a source
incompatibility in Hive and was removed from branch-2. Not sure if this would cause problems
at runtime if an application with the old version was deployed on the new version. Will look
into it. Details in HADOOP-13338.

FileStatus also still implements Comparable but specifies it's own type. It requires a FileStatus,
not an Object, although it used to cast the Object to a FileStatus anyway. So the only this
would actually fail is if someone was casting a FileStatus to an Object before the call to
compare(). So it could happen, but it's unlikely, and fixing that is something someone could
do before upgrading to Hadoop 3. That change was in https://issues.apache.org/jira/browse/HADOOP-12209.
I'm inclined to fix that by documentating that we support rolling upgrade, assuming a set
of things have been checked, including that.

> Support rolling upgrade between 2.x and 3.x
> -------------------------------------------
>
>                 Key: HDFS-11096
>                 URL: https://issues.apache.org/jira/browse/HDFS-11096
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: rolling upgrades
>    Affects Versions: 3.0.0-alpha1
>            Reporter: Andrew Wang
>            Priority: Blocker
>
> trunk has a minimum software version of 3.0.0-alpha1. This means we can't rolling upgrade
between branch-2 and trunk.
> This is a showstopper for large deployments. Unless there are very compelling reasons
to break compatibility, let's restore the ability to rolling upgrade to 3.x releases.



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