public static void setKeyAndValueDesc(ReduceWork work, ReduceSinkOperator rs) {
    work.setKeyDesc(rs.getConf().getKeySerializeInfo());
    int tag = Math.max(0, rs.getConf().getTag());
    List<TableDesc> tagToSchema = work.getTagToValueDesc();
    while (tag + 1 > tagToSchema.size()) {
      tagToSchema.add(null);
    }
    tagToSchema.set(tag, rs.getConf().getValueSerializeInfo());
  }
Set key and value descriptor
@param work RedueWork
@param rs ReduceSinkOperator
ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMapRedUtils.java