public List<DirDiff> getSubDirsAdded() {
    return subDirsAdded;
  }
Subdirectories that are already present in the previous snapshot, but don't exist in the local snapshot,
and hence all of their contents need to be recursively removed.
samza-core/src/main/java/org/apache/samza/storage/blobstore/diff/DirDiff.java