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From "Keith Turner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-769) MapReduce API should not use Configuration to set Job state at submission time (ambiguous semantics)
Date Thu, 20 Sep 2012 18:10:07 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-769?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13459813#comment-13459813
] 

Keith Turner commented on ACCUMULO-769:
---------------------------------------

I am not a big fan of the churn in the API this change would make.  However I do agree with
the goal of this ticket.  This leaves me a bit conflicted on this issue.  Passing in a Job
removes the possibility that the user will do something wrong.  With the new API in 1.4 the
user can write the following code that is incorrect.  

{code:java}
  @Override
  public int run(String[] args) throws Exception {

    Configuration conf = getConf();
    Job job = new Job(conf, "Test MR 1");
      .
      .
      .
    job.setOutputFormatClass(AccumuloOutputFormat.class);
    AccumuloOutputFormat.setOutputInfo(conf, "root", "secret".getBytes(), false, "nodes");
 //WRONG, modifying conf will not setup the job
  }
{code}

Instead the user needs to write the following with the new API

{code:java}
  @Override
  public int run(String[] args) throws Exception {

    Configuration conf = getConf();
    Job job = new Job(conf, "Test MR 1");
      .
      .
      .
    job.setOutputFormatClass(AccumuloOutputFormat.class);
    AccumuloOutputFormat.setOutputInfo(job.getConfiguration(), "root", "secret".getBytes(),
false, "nodes");  //CORRECT, modifying the job conf will setup the job
  }
{code}

If the user just passed in the job object they would not have to think about it and understand
that job creates a copy of the config they passed.    


                
> MapReduce API should not use Configuration to set Job state at submission time (ambiguous
semantics)
> ----------------------------------------------------------------------------------------------------
>
>                 Key: ACCUMULO-769
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-769
>             Project: Accumulo
>          Issue Type: Bug
>          Components: client
>    Affects Versions: 1.4.1, 1.4.0
>            Reporter: Christopher Tubbs
>            Assignee: Billie Rinaldi
>            Priority: Minor
>             Fix For: 1.5.0
>
>
> ACCUMULO-267 made this change, but I think it was the wrong way to go about it.
> From the comments on ACCUMULO-267:
> This is the wrong way to go about doing this fix. The reason why it took a JobContext
is so that it could accept a "Job" object. This was modeled after the pattern Hadoop was using
for FileOutputFormat, which is somewhat the standard for conventions in configuring MR jobs.
> While JobContext does specifically state that's what it's purpose is, it is a base class,
and Job extends JobContext, and includes a comment that describes it as holding the state
of the job at submission time. This API should really be taking a "Job" object, rather than
a "JobContext" object. Further, because Job is the only JobContext that actually works as
intended here, the change from JobContext to Job does not require any deprecation, because
Job will still work, and any other JobContext that isn't a Job will still fail. (We would
have to deprecate the ones that were added in 1.4 that took a Configuration object, though...
because those were never "correct", if we are going off of the conventions set by Hadoop's
provided OutputFormats).
> It is somewhat annoying to deprecate something in 1.5 that was added in 1.4... especially
since it allows people to go back to what they were doing before. But, I think it might be
worth it to be consistent with the established conventions, and to clarify the semantics of
the methods (we are, after all, modifying the state of a job we are about to submit, and not
just an arbitrary configuration, which is used for all sorts of things).

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