@Override
  public Iterable<Object> getCurrentValues() throws IOException {
    kvsIterable.init(nextKVReaders);
    return kvsIterable;
  }
@return true if there are more key-values and advances to next key-values
@throws IOException
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/tools/KeyValuesInputMerger.java