@Override
    public String toString() {
      return "Stats{" +
          "filesAdded=" + filesAdded +
          ", filesRetained=" + filesRetained +
          ", filesRemoved=" + filesRemoved +
          ", subDirsAdded=" + subDirsAdded +
          ", subDirsRetained=" + subDirsRetained +
          ", subDirsRemoved=" + subDirsRemoved +
          ", bytesAdded=" + bytesAdded +
          ", bytesRetained=" + bytesRetained +
          ", bytesRemoved=" + bytesRemoved +
          '}';
    }
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