Using a custom Object as key emitted by mapper - hadoop

Question

I have a situation in which mapper emits as key an object of custom type.
It has two fields an intWritable ID, and a data array IntArrayWritable.
The implementation is as follows.
`
import java.io.*;
import org.apache.hadoop.io.*;
public class PairDocIdPerm implements WritableComparable<PairDocIdPerm> {
public PairDocIdPerm(){
this.permId = new IntWritable(-1);
this.SignaturePerm = new IntArrayWritable();
}
public IntWritable getPermId() {
return permId;
}
public void setPermId(IntWritable permId) {
this.permId = permId;
}
public IntArrayWritable getSignaturePerm() {
return SignaturePerm;
}
public void setSignaturePerm(IntArrayWritable signaturePerm) {
SignaturePerm = signaturePerm;
}
private IntWritable permId;
private IntArrayWritable SignaturePerm;
public PairDocIdPerm(IntWritable permId,IntArrayWritable SignaturePerm) {
this.permId = permId;
this.SignaturePerm = SignaturePerm;
}
#Override
public void write(DataOutput out) throws IOException {
permId.write(out);
SignaturePerm.write(out);
}
#Override
public void readFields(DataInput in) throws IOException {
permId.readFields(in);
SignaturePerm.readFields(in);
}
#Override
public int hashCode() { // same permId must go to same reducer. there fore just permId
return permId.get();//.hashCode();
}
#Override
public boolean equals(Object o) {
if (o instanceof PairDocIdPerm) {
PairDocIdPerm tp = (PairDocIdPerm) o;
return permId.equals(tp.permId) && SignaturePerm.equals(tp.SignaturePerm);
}
return false;
}
#Override
public String toString() {
return permId + "\t" +SignaturePerm.toString();
}
#Override
public int compareTo(PairDocIdPerm tp) {
int cmp = permId.compareTo(tp.permId);
Writable[] ar, other;
ar = this.SignaturePerm.get();
other = tp.SignaturePerm.get();
if (cmp == 0) {
for(int i=0;i<ar.length;i++){
if(((IntWritable)ar[i]).get() == ((IntWritable)other[i]).get()){cmp= 0;continue;}
else if(((IntWritable)ar[i]).get() < ((IntWritable)other[i]).get()){ return -1;}
else if(((IntWritable)ar[i]).get() > ((IntWritable)other[i]).get()){return 1;}
}
}
return cmp;
//return 1;
}
}`
I require the keys with same Id to go to the same reducer with their sort order as coded in the compareTo method.
However when i use this, my job execution status is always map100% reduce 0%.
The reduce never runs to completion. Is there any thing wrong in this implementation?
In general what is the likely problem if reducer status is always 0%.

Answer 1

I think this might be a possible null pointer exception in the read method:
#Override
public void readFields(DataInput in) throws IOException {
permId.readFields(in);
SignaturePerm.readFields(in);
}
permId is null in this case.
So what you have to do is this:
IntWritable permId = new IntWritable();
Either in the field initializer or before the read.
However, your code is horrible to read.