@Override
 public PTableType<K, V> getPTableType() {
   return source.getTableType();
 }
 @Override
 public PType<Pair<K, V>> getPType() {
   return source.getType();
 }
 public InputTable(TableSource<K, V> source, MRPipeline pipeline) {
   super(source.toString());
   this.source = source;
   this.pipeline = pipeline;
   this.asCollection = new InputCollection<Pair<K, V>>(source, pipeline);
 }