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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