@Override
    public Iterator<Entry<Long, ByteBuffer>> getFileMetadata(
        List<Long> fileIds) throws HiveException {
      return hive.getFileMetadata(fileIds).iterator();
    }
An implementation of external cache and factory based on metastore.
ql/src/java/org/apache/hadoop/hive/ql/io/orc/MetastoreExternalCachesByConf.java