[ https://issues.apache.org/jira/browse/MRUNIT-165?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Yoni Ben-Meshulam updated MRUNIT-165:
-------------------------------------

    Description: 
MapReduceDriver calls the Mapper#run method for each input, causing the Mapper#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 StatefulMapper 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(this.someState));
    }

}
{code}

  was:
MapReduceDriver calls the Mapper#run method for each input, causing the Mapper#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(this.someState));
    }

}
{code}

    
> 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 Mapper#run method for each input, causing the Mapper#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 StatefulMapper 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(this.someState));
>     }
> }
> {code}

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