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https://issues.apache.org/jira/browse/HADOOP-9517?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13660318#comment-13660318
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Steve Loughran commented on HADOOP-9517:
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There's two extra forms of compatibility we should define and document
h3. Source code compatibility
Whether or not a patch will apply across versions. I'm tempted to make no
guarantees across major versions (what we have today w.r.t 1.x and 2.x), and a
"no deliberate attempt to break things", policy, but otherwise: you are on your
own if you fork the code and try to cherry pick, or try to have private patches
to apply on top of the source tree. "The best way to ensure your patches stay
in sync with the code is to get them into the Apache source tree".
h3. Configuration compatibility.
Whether configuration parameters will be consistent over versions; whether, if
the names change, there will be a transition from one version to the other.
This happens today, with warnings on deprecation -which should be called out.
"When warned, fix". Similarly, whether defaults change between major/minor
releases. I'd say "sometimes", as it is becoming time to increase the default
block size, the default #of reducers and a few more.
> Define Hadoop Compatibility
> ---------------------------
>
> Key: HADOOP-9517
> URL: https://issues.apache.org/jira/browse/HADOOP-9517
> Project: Hadoop Common
> Issue Type: Bug
> Components: documentation
> Reporter: Arun C Murthy
> Assignee: Karthik Kambatla
> Attachments: hadoop-9517.patch, hadoop-9517.patch, hadoop-9517.patch,
> hadoop-9517.patch
>
>
> As we get ready to call hadoop-2 stable we need to better define 'Hadoop
> Compatibility'.
> http://wiki.apache.org/hadoop/Compatibility is a start, let's document
> requirements clearly and completely.
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