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