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http://issues.apache.org/jira/browse/HADOOP-80?page=comments#action_12370606 ] 

Doug Cutting commented on HADOOP-80:
------------------------------------

If we think that the default java hash function is bad, then we should probably 
switch it in all of the places where we hash, e.g., in UTF8, here, etc.  For 
now I will: (a) add a static hashBytes() method to WritableComparable, use it 
in BytesWritable().  Then, if we someday decide to change the hash function 
then we'll have a single place to do it.  Allocating a new digester per call to 
hashCode() seems expensive (although I have not benchmarked this).

MapReduce does use the hash function by default for partitioning, but HashMaps 
will also use it, so MapReduce is not the only client.

> binary key
> ----------
>
>          Key: HADOOP-80
>          URL: http://issues.apache.org/jira/browse/HADOOP-80
>      Project: Hadoop
>         Type: New Feature
>   Components: io
>     Versions: 0.1
>     Reporter: Owen O'Malley
>     Assignee: Owen O'Malley
>      Fix For: 0.1
>  Attachments: binary-key-2.patch, binary-key.patch
>
> I needed a binary key type, so I extended BytesWritable to be comparable also.

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