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From "Jingkei Ly (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-3378) Incorrect sort order if WritableComparable.compareTo() does not return -1, 0 or 1
Date Tue, 13 May 2008 10:18:55 GMT
Incorrect sort order if WritableComparable.compareTo() does not return -1, 0 or 1
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                 Key: HADOOP-3378
                 URL: https://issues.apache.org/jira/browse/HADOOP-3378
             Project: Hadoop Core
          Issue Type: Bug
          Components: io
    Affects Versions: 0.16.3
            Reporter: Jingkei Ly
            Priority: Minor


I've found that incorrect sort orders are returned in some cases if the WritableComparable.compareTo()
method doesn't return  -1, 0 or 1. 

I believe this is a bug as the compareTo() interface states that the returned int be only
a -ve or +ve number, and will potentially catch a lot of people out who decide to write a
WritableComparator (well it caught me out anyway!). 

I'll attach an example application to demonstrate -- I simply modified the sort example to
specify a non-default comparator to sort LongWritable , i.e.:

public int compare(WritableComparable a, WritableComparable b)	{
	LongWritable longA =(LongWritable) a;
	LongWritable longB =(LongWritable) b;
	
	return (int) (longA.get() - longB.get());  // wrong sort order
	// return (int) Math.signum(longA.get() - longB.get());  // correct sort order
}

When I run the application through Hadoop on my input data it returns the incorrect sort order.

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