QMDB REVERT

[NikhilSharmaWe]

Description

QMDB does not have the functionality of reverting the state. If someone needs to implement reverting state functionality in QMDB, what should be the approach for implementing such a feature, to revert to the preceding commit immediately?

[absolute0kelvin]

If you just want to revert to a state which is N blocks earlier, it's much easier to implement an in-memory overlay to cache the changes of last N blocks. When a block has N confirmations we flush its changes to QMDB. Any read will firstly be checked against this overlay before going to qmdb. Reverting is just remove a block from the overlay.

[NikhilSharmaWe]

Yes, but in addition to the data, I also want to calculate the state roots and state proofs considering the in-memory changes.