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https://issues.apache.org/jira/browse/HADOOP-11656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15982254#comment-15982254
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Christopher Tubbs commented on HADOOP-11656:
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[~busbey] Thanks for the excellent summary! It helps put all this in context.
As for:
bq. Given the above background information about the old features and the
client-side features under discussion, why would we publish the non-shaded
version of any of the three shaded and relocated jars?
If these expose the same API with the same class names, then I cannot think of
any reason. In that case, this is equivalent to a shaded classifier version
(albeit, without the clear marking as having been shaded). If there's any
difference in the API at all, then all the usual reasons somebody might avoid
shaded jars would also apply to these. From what I saw in the POMs, they don't
look like they are adding new API, just shading existing APIs in... which seems
fine to me, provided none of the relocated dependencies are exposed in the APIs.
I would say that it is atypical to do the shading in a separate module rather
than a classifier, and that's a little confusing and surprising, but it's not
at all "wrong" to do so.
Also, no need to apologize. I have felt nothing but patience and positive
responses to my questions and observations in this thread. Thanks for that!
> Classpath isolation for downstream clients
> ------------------------------------------
>
> Key: HADOOP-11656
> URL: https://issues.apache.org/jira/browse/HADOOP-11656
> Project: Hadoop Common
> Issue Type: New Feature
> Reporter: Sean Busbey
> Assignee: Sean Busbey
> Priority: Blocker
> Labels: classloading, classpath, dependencies, scripts, shell
> Attachments: HADOOP-11656_proposal.md
>
>
> Currently, Hadoop exposes downstream clients to a variety of third party
> libraries. As our code base grows and matures we increase the set of
> libraries we rely on. At the same time, as our user base grows we increase
> the likelihood that some downstream project will run into a conflict while
> attempting to use a different version of some library we depend on. This has
> already happened with i.e. Guava several times for HBase, Accumulo, and Spark
> (and I'm sure others).
> While YARN-286 and MAPREDUCE-1700 provided an initial effort, they default to
> off and they don't do anything to help dependency conflicts on the driver
> side or for folks talking to HDFS directly. This should serve as an umbrella
> for changes needed to do things thoroughly on the next major version.
> We should ensure that downstream clients
> 1) can depend on a client artifact for each of HDFS, YARN, and MapReduce that
> doesn't pull in any third party dependencies
> 2) only see our public API classes (or as close to this as feasible) when
> executing user provided code, whether client side in a launcher/driver or on
> the cluster in a container or within MR.
> This provides us with a double benefit: users get less grief when they want
> to run substantially ahead or behind the versions we need and the project is
> freer to change our own dependency versions because they'll no longer be in
> our compatibility promises.
> Project specific task jiras to follow after I get some justifying use cases
> written in the comments.
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