public void mergeAliasedInput(String alias, Path pathDir, PartitionDesc partitionInfo) {
    StringInternUtils.internUriStringsInPath(pathDir);
    alias = alias.intern();
    List<String> aliases = pathToAliases.get(pathDir);
    if (aliases == null) {
      aliases = new ArrayList<>(Arrays.asList(alias));
      pathToAliases.put(pathDir, aliases);
      pathToPartitionInfo.put(pathDir, partitionInfo);
    } else {
      aliases.add(alias);
    }
  }
For each map side operator - stores the alias the operator is working on
behalf of in the operator runtime state. This is used by reduce sink
operator - but could be useful for debugging as well.
ql/src/java/org/apache/hadoop/hive/ql/plan/MapWork.java