There's a snapshot based fast-sync mechanism that restores the UTXO database. It was described in UIP-11. Although it's implemented and tested, it doesn't work in a real-life because during fast-sync we lose all the finalization information.
There's also a way of a finalization state exchange that was described in UIP-21. Presently it's used in full-sync only to provide additional input for the fork-choice rule (UIP-12). However, it can be used for the fast-sync purpose as well.
Steps to make integration work:
[x] Add Commits Merkle Root to the header as described in UIP-21. (#815).
[x] Get rid of FROM_COMMITS status in finalization exchange or make it as good as COMPLETED (follow the link for details). (#844).
[x] Add glue code in between and write tests. (#852, #856).
[x] Review and cleanup #836 references in the code base (#911).
There's a snapshot based fast-sync mechanism that restores the UTXO database. It was described in UIP-11. Although it's implemented and tested, it doesn't work in a real-life because during fast-sync we lose all the finalization information.
There's also a way of a finalization state exchange that was described in UIP-21. Presently it's used in full-sync only to provide additional input for the fork-choice rule (UIP-12). However, it can be used for the fast-sync purpose as well.
Steps to make integration work:
#836references in the code base (#911).