[jira] Resolved: (HADOOP-3378) Incorrect sort order if WritableComparable.compareTo() does not return -1, 0 or 1

["Chris Douglas (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-3378?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Chris Douglas resolved HADOOP-3378.
-----------------------------------

    Resolution: Invalid

The problem with your example is the cast to {{int}} in the comparator. If longA - longB > Integer.MAX_VALUE, then it'll overflow and return a negative number.

> Incorrect sort order if WritableComparable.compareTo() does not return -1, 0 or 1
> ---------------------------------------------------------------------------------
>
>                 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
>         Attachments: hadoop-bug.csv, Sort.java
>
>
> 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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