@Override
  public String toString() {
    if (aliasBucketFileNameMapping != null) {
      return "Mapping:" + aliasBucketFileNameMapping.toString();
    } else {
      return "";
    }
  }
was inner class of MapreLocalWork. context for bucket mapjoin (or smb join)
ql/src/java/org/apache/hadoop/hive/ql/plan/BucketMapJoinContext.java