[MAHOUT-937] Collocations Job Partitioner not being configured properly

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.5
• Fix Version/s: 0.6
• Assignee: Sean R. Owen
• Reporter: Mat Kelcey
• Created: 28/Dec/11 06:29
• Updated: 09/Feb/12 14:00
• Resolved: 29/Dec/11 03:21

Description

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...

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;    
  }
  
}