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https://issues.apache.org/jira/browse/MAHOUT-937?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen updated MAHOUT-937:
-----------------------------
Attachment: MAHOUT-937.patch
> Collocations Job Partitioner not being configured properly
> ----------------------------------------------------------
>
> Key: MAHOUT-937
> URL: https://issues.apache.org/jira/browse/MAHOUT-937
> Project: Mahout
> Issue Type: Bug
> Affects Versions: 0.5
> Reporter: Mat Kelcey
> Assignee: Sean Owen
> Priority: Minor
> Fix For: 0.6
>
> Attachments: GramKeyPartitioner.java, MAHOUT-937.patch
>
>
> The first pass of the collocations discovery job (as described by
> CollocDriver.generateCollocations) uses the
> org.apache.mahout.vectorizer.collocations.llr.GramKeyPartitioner partitioner.
> This partitoner has an instance variable offset that is supposed to be set by
> a call to setOffsets() but this call is never made (not sure why? is this
> method expected to be called by the Hadoop framework itself?)
> The offset not being set results in getPartition always returning 0 and so
> all intermediate data is sent to the one reducer.
> I couldn't quite understand what this partitioning was meant to be doing, but
> simply hashing the Grams primary string representation (ie without the
> leading 'type' byte) does what is required...
> {code}
> public class GramKeyPartitioner extends Partitioner<GramKey, Gram> {
> @Override
> public int getPartition(GramKey key, Gram value, int numPartitions) {
> // exclude first byte which is the key type
> byte[] keyBytesWithoutTypeByte = new byte[key.getPrimaryLength()-1];
> System.arraycopy(key.getBytes(), 1, keyBytesWithoutTypeByte, 0,
> keyBytesWithoutTypeByte.length);
> int hash = WritableComparator.hashBytes(keyBytesWithoutTypeByte,
> keyBytesWithoutTypeByte.length);
> return (hash & Integer.MAX_VALUE) % numPartitions;
> }
>
> }
> {code}
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