If you have existing MapReduce v1 jobs from a hadoop 1.x cluster that you want to run in the 4.0.x cluster, you may need to recompile the MapReduce jobs.
If your MapReduce v1 job contains the following API, you may need to recompile the job prior to running the job in the 4.0.x cluster:
|MapReduce Job API||Source Compatibility||Binary Compatibility||Recompile Required?|
|org.apache.hadoop.mapred||Yes||Partial||If Job, JobControl, or JobContext classes are used, then the code requires minor updates and a recompile due to API changes.|
|org.apache.hadoop.mapreduce||Yes||No||Recompilation is required.|
To recompile a MapReduce v1 job:
Run the following command:
javac -cp $(/opt/mapr/hadoop/hadoop-0.20.2/bin/hadoop classpath) <java.program>