There are a number of classes under mapreduce.lib that are not present in the 1.x series. Including these would help users and downstream projects using the new MapReduce API migrate to later versions of Hadoop in the future.
A few examples of where this would help:
- Sqoop uses mapreduce.lib.db.DBWritable and mapreduce.lib.input.CombineFileInputFormat (
- Mahout uses mapreduce.lib.output.MultipleOutputs (
- HBase has a backport of mapreduce.lib.partition.InputSampler and TotalOrderPartitioner (in org.apache.hadoop.hbase.mapreduce.hadoopbackport) - it would be better if it used the ones in Hadoop.