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https://issues.apache.org/jira/browse/HADOOP-11656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15982221#comment-15982221
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Sean Busbey commented on HADOOP-11656:
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I'm in the middle of familial responsibilities, so my apologies in advance if
this comes off as curt [~ctubbsii].
I believe [~sjlee0]'s question above is basically "I didn't realize we'd be
publishing shaded jars into Maven Central, could we skip doing that?"
([~sjlee0], please correct me if I'm wrong.)
The answer to this, as I stated above, is no because then folks relying on the
shaded version could not test as a part of normal maven lifecycle.
If you look at the code as of the 3.0.0-alpha2 release, you will see that we
have the following modules:
* hadoop-client - a neither shaded nor relocated module that claims to expose
just those hadoop and transitive dependency artifacts needed to interact with a
client (this has been in the code base since roughly hadoop 1.0). Anyone
wanting non-shaded access to Hadoop and its dependencies can continue to use
this artifact.
* hadoop-minicluster - a neither shaded nor relocated test module that provides
tools needed to test the above (also since roughly Hadoop 1.0)
* hadoop-client-api - a shaded and relocated module containing Hadoop authored
classes needed to compile a client. (If you look at the code or read the
relevant jira, it explains that this is generated via part of the above
hadoop-client module and is new for 3.0.0-alpha2)
* hadoop-client-runtime - a companion shaded and relocated module containing
Hadoop and third party classes needed to run client built using the above api
jar. (also generated via part of the hadoop-cliet module and also new for
3.0.0-alpha2)
* hadoop-client-minicluster - a shaded and relocated version of the
hadoop-minicluster module above that can be used to test the shade-relocated
client modules above
* invariant tests and integration tests for the above generated modules, which
require said modules in order to be checked.
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?
> 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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