@Override
      public void write(WritableComparable<?> key, BytesRefArrayWritable value)
        throws IOException {
        out.append(value);
      }
Set number of columns into the given configuration.
@param conf
         configuration instance which need to set the column number
@param columnNum
         column number for RCFile's Writer
hcatalog/core/src/main/java/org/apache/hive/hcatalog/rcfile/RCFileMapReduceOutputFormat.java