@Signature
  @Explain(displayName = "sort order", explainLevels = { Level.DEFAULT, Level.EXTENDED })
  public String getOrder() {
    return keySerializeInfo.getProperties().getProperty(
        org.apache.hadoop.hive.serde.serdeConstants.SERIALIZATION_SORT_ORDER);
  }
Returns the sort order of the key columns.

@return null, which means ascending order for all key columns, or a String
        of the same length as key columns, that consists of only "+"
        (ascending order) and "-" (descending order).
ql/src/java/org/apache/hadoop/hive/ql/plan/ReduceSinkDesc.java