private static ParsedDelta parsedDelta(Path deltaDir, FileSystem fs, HdfsDirSnapshot dirSnapshot)
      throws IOException {
    ParsedDeltaLight deltaLight = ParsedDeltaLight.parse(deltaDir);
    //small optimization - delete delta can't be in raw format
    boolean isRawFormat = !deltaLight.isDeleteDelta && MetaDataFile.isRawFormat(deltaDir, fs, dirSnapshot);
    List<HdfsFileStatusWithId> files = null;
    if (dirSnapshot != null) {
      final PathFilter filter = isRawFormat ? AcidUtils.originalBucketFilter : AcidUtils.bucketFileFilter;
      // If we already know the files, store it for future use
      files = dirSnapshot.getFiles().stream()
          .filter(fileStatus -> filter.accept(fileStatus.getPath()))
          .map(HdfsFileStatusWithoutId::new)
          .collect(Collectors.toList());
    }
    return new ParsedDelta(deltaLight, isRawFormat, files);
  }
This will look at a footer of one of the files in the delta to see if the
file is in Acid format, i.e. has acid metadata columns.  The assumption is
that for any dir, either all files are acid or all are not.
ql/src/java/org/apache/hadoop/hive/ql/io/AcidUtils.java