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From "Age Mooij (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1842) JobID.forName() creates JobID instances that break equality
Date Fri, 04 Jun 2010 12:18:55 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1842?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12875575#action_12875575
] 

Age Mooij commented on MAPREDUCE-1842:
--------------------------------------

By the way, I mentioned that I thought JobId is not Serializable and that's why I ran into
this problem. As a workaround we now use the readFields and writeFields methods to serialize
our JobID instances, which is of course the preferred way.

The forName/equals code is still broken though.

> JobID.forName() creates JobID instances that break equality
> -----------------------------------------------------------
>
>                 Key: MAPREDUCE-1842
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1842
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: job submission
>    Affects Versions: 0.20.2
>            Reporter: Age Mooij
>
> We have some code that uses serialization to store org.apache.hadoop.mapreduce.JobID
instances (among other things). Since org.apache.hadoop.mapreduce.JobID is not serializable,
we store the String representation and use org.apache.hadoop.mapreduce.JobID.forName(String)
to read it back.
> Unfortunately the instance created by that method is not equal to the same id as created
by the constructor. Here's a unit test for the problem:
> @Test
> public void forNameCopyShouldProduceInstanceEqualToOriginal() {
>     JobID jobId1 = new JobID("original", 1);
>     JobID jobId2 = JobID.forName(jobId1.toString());
>     assertEquals(jobId1, jobId2);
> }
> forName(String) produces a backwards compatible instance from the old mapred package
but the equals method shared by them both uses this.getClass() == that.getClass() and that
causes the incompatible instances.
> I know this backwards compatible stuff is important but could you please fix this ? The
simplest fix would be to change the implementation of equals() or override it in the backwards
compatibillity version of JobID in the old mapred package

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