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https://issues.apache.org/jira/browse/HDFS-5535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13866405#comment-13866405
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Arpit Agarwal commented on HDFS-5535:
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{quote}
This means even changing the internal protocols also breaks the compatibility.
In that case have to wait for major releases..? or add overloaded apis..?
{quote}
It is often possible to change protocols incrementally without breaking
compatibility. Usually this means *a.* not adding or removing any required
fields (required fields are considered bad for this reason); *b.* not adding or
changing the meaning of any optional fields in such a way as to break a peer
running an older version and *c.* some protocol changes may have to be
introduced in an incremental manner across two minor releases, i.e. release n+1
adds support for handling protocol changes to be introduced in release n+2.
Note that the doc mentions rolling upgrades must be possible between
consecutive minor releases only.
The last is per my understanding, I don't want to speak for the design authors.
> Umbrella jira for improved HDFS rolling upgrades
> ------------------------------------------------
>
> Key: HDFS-5535
> URL: https://issues.apache.org/jira/browse/HDFS-5535
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: datanode, ha, hdfs-client, namenode
> Affects Versions: 3.0.0, 2.2.0
> Reporter: Nathan Roberts
> Attachments: HDFSRollingUpgradesHighLevelDesign.pdf
>
>
> In order to roll a new HDFS release through a large cluster quickly and
> safely, a few enhancements are needed in HDFS. An initial High level design
> document will be attached to this jira, and sub-jiras will itemize the
> individual tasks.
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