Mojang wrote a DFU system called Data Fixer Upper. It is open source, peggs the CPU at 100% on startup for about a minute, doubles game launch time, references

Mojang wrote a DFU system called Data Fixer Upper. It is open source, peggs the CPU at 100% on startup for about a minute, doubles game launch time, references 10 research papers, sometimes corrupts the world, and is so abstract only the author knows how it works - all to upgrade game worlds to new versions. It is often called Data Fucker Upper.