@Explain(displayName = "Alias Bucket Base File Name Mapping", explainLevels = { Level.EXTENDED })
  public Map<String, Map<String, List<String>>> getAliasBucketBaseFileNameMapping() {
    return aliasBucketBaseFileNameMapping;
  }
was inner class of MapreLocalWork. context for bucket mapjoin (or smb join)
ql/src/java/org/apache/hadoop/hive/ql/plan/BucketMapJoinContext.java