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