code: public void setSpecificOrderBy(String schemaName, OrderBy ordering)
        throws TupleMRException {
      // TODO
      failIfNull(schemaName, "Not able to set specific orderBy for null source");
      if (!schemaAlreadyExists(schemaName)) {
        throw new TupleMRException("Unknown source '" + schemaName
            + "' in specific OrderBy");
      }
      failIfNull(ordering, "Not able to set null criteria for source '" + schemaName + "'");
      failIfEmpty(ordering.getElements(), "Can't set empty ordering");
      failIfNull(commonOrderBy,
          "Not able to set specific order with no previous common OrderBy");
      if (commonOrderBy.getSchemaOrderIndex() == null) {
        throw new TupleMRException(
            "Need to specify source order in common OrderBy when using specific OrderBy");
      }
      if (ordering.getSchemaOrderIndex() != null) {
        throw new TupleMRException("Not allowed to set source order in specific order");
      }
      Schema schema = getSchemaByName(schemaName);
      Map<String, String> aliases = fieldAliases.get(schema.getName());
      for (SortElement e : ordering.getElements()) {
        if (!Schema.containsFieldUsingAlias(schema, e.getName(), aliases)) {
          throw new TupleMRException("Source '" + schemaName + "' doesn't contain field '"
              + e.getName());
        }
        if (e.getCustomComparator() != null) {
          Field field = schema.getField(e.getName());
          if (field == null) {
            field = schema.getField(aliases.get(e.getName()));
          }
          if (field.getType() != Type.OBJECT) {
            throw new TupleMRException("Not allowed to set custom comparator for type=" + field.getType());
          }
        }
      }
  
      for (SortElement e : ordering.getElements()) {
        if (commonOrderBy.containsFieldName(e.getName())) {
          throw new TupleMRException("Common sort by already contains sorting for field '"
              + e.getName());
        }
      }
      this.specificsOrderBy.put(schemaName, ordering);
    }
docs: Sets how tuples from the specific schemaName will be sorted after being
  sorted by commonOrderBy and schemaOrder