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https://issues.apache.org/jira/browse/HADOOP-9902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13907228#comment-13907228
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Allen Wittenauer commented on HADOOP-9902:
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Let's talk about the 'classpath' subcommand.
Today, hadoop classpath returns the classpath of common, hdfs, and yarn. To
me, this seems to be the wrong behavior for a two major reasons:
* Common has to have to knowledge about subsystems that rely upon it.
Ultimately, this is a reverse dependency and (I hope) we can all agree those
are bad.
* If I'm building an application that only needs access to
(common|hdfs|yarn|mapreduce), my classpath is polluted with extra garbage from
the other subproject(s) that may or may not need. (yarn does offer a classpath
subcommand but it's essentially the same thing as the hadoop classpath. The
mapreduce classpath is... yeah...)
On the plus side, it's one stop shopping. "Hooray! I get everything!", some
developer likely said somewhere.
So I'd like to throw out a proposal.
I want to re-implement the classpath subcommand such that (hadoop|hdfs|yarn)
only return the base classpath for their project. This is (obviously) an
incompatible change. Someone who wanted to know what all the classpaths were
for all the projects would be required to run all the commands.
To make up for it, however, I believe I can *easily* introduce a classpath
subcommand for *every* command that uses the common framework. For the
non-major commands, I suspect this would be a massive win for debugging. "What
the heck is start-dfs.sh using when it fires up the namenode?", said myself
many many times but using more curse words, some of which you might not have
heard before.
Another choice might be to have some tricky logic to have subprojects
'register' into the main project on install such that commands like 'hadoop
classpath' now know about those subprojects. It won't solve the second bullet
point, but it does fix the first.
Thoughts?
> Shell script rewrite
> --------------------
>
> Key: HADOOP-9902
> URL: https://issues.apache.org/jira/browse/HADOOP-9902
> Project: Hadoop Common
> Issue Type: Improvement
> Components: scripts
> Affects Versions: 3.0.0, 2.1.1-beta
> Reporter: Allen Wittenauer
> Assignee: Allen Wittenauer
> Attachments: HADOOP-9902.txt, hadoop-9902-1.patch, more-info.txt
>
>
> Umbrella JIRA for shell script rewrite. See more-info.txt for more details.
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