private void processPpdResult(MetadataPpdResult mpr, HdfsFileStatusWithId file,
      int ix, OrcTail[] result, ByteBuffer[] ppdResult) throws IOException {
    if (mpr == null)
     {
      return; // This file is unknown to metastore.
    }

    ppdResult[ix] = mpr.isSetIncludeBitset() ? mpr.bufferForIncludeBitset() : NO_SPLIT_AFTER_PPD;
    if (mpr.isSetMetadata()) {
      result[ix] = createOrcTailFromMs(file, mpr.bufferForMetadata());
      if (result[ix] != null) {
        localCache.put(file.getFileStatus().getPath(), result[ix]);
      }
    }
  }
Metastore-based footer cache storing serialized footers. Also has a local cache.
ql/src/java/org/apache/hadoop/hive/ql/io/orc/ExternalCache.java