Yoni Ben-Meshulam created MRUNIT-165:
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Summary: MapReduceDriver calls Mapper#cleanup for each input
instead of once
Key: MRUNIT-165
URL: https://issues.apache.org/jira/browse/MRUNIT-165
Project: MRUnit
Issue Type: Bug
Affects Versions: 0.9.0
Reporter: Yoni Ben-Meshulam
MapReduceDriver calls the {{run}} method for each input, causing the
{{cleanup}} method to be called multiple times.
I believe this is a bug, since the contract in MapReduce is that, for a single
Mapper instance, the {{Mapper#cleanup}} method is only called once after all
inputs to that mapper have been processed. I might be mistaken in my assumption
here.
This would not be an issue, were it not for the fact that MapReduceDriver has
only a single instance of Mapper.
One solution might be to pass the Mapper _class_ into the MapReduceDriver and
create a new instance for each input. Another solution might be to call the
MapDriver with multiple inputs (which AFAIK is not possible).
----
To reproduce, create a MapReduce job with some stateful mapper:
{code}
public class ClosedFormRegressionMapper extends Mapper<LongWritable, Text,
Text, IntWritable> {
public static final Text KEY = new Text("SomeKey");
private Int someState = 0;
/**
* Increment someState for each input.
*
* @param context the Hadoop job Map context
* @throws java.io.IOException
*/
@Override
public void map(
LongWritable key,
Text value,
Context context
) throws IOException, InterruptedException {
this.someState += 1;
}
/**
* Runs once after all maps have occurred. Dumps the accumulated state to
the output.
* @param context the Hadoop job Map context
*/
@Override
protected void cleanup(Context context) throws IOException,
InterruptedException {
context.write(this.KEY, new IntWritable(someState));
}
}
{code}
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