code: public void write(DataOutput out) throws IOException {
      out.writeInt(getLayoutVersion());
      out.writeInt(getNamespaceID());
      out.writeLong(getCTime());
      out.writeLong(mostRecentCheckpointTxId);
      out.writeLong(curSegmentTxId);
      imageDigest.write(out);
    }
docs: ///////////////////////////////////////////////