@Override
  public String toString() {
    return "FileBlob{" + "blobId='" + blobId + '\'' + ", offset=" + offset + '}';
  }
Offset of this blob in the file. A file can be uploaded multiple chunks, and can have
multiple blobs associated with it. Each blob then has its own ID and an offset in the file.
samza-core/src/main/java/org/apache/samza/storage/blobstore/index/FileBlob.java