MemoryOverlay on top of QMDB

[NikhilSharmaWe]

Description

I'm working on QMDB and looking to implement something like MemoryOverlayState on top of the ADS. The goal is to store changes in-memory and perform state root and proof calculations without committing or flushing the state to the ADS.

I explored SeqADS, which is designed for this use case using the stateless crate and WitnessUpdater. However, ADS and SeqADS can't be used simultaneously due to concurrent access to the same tree files. Creating a copy of the data files is possible, but it would be too expensive. An alternative could be to implement a memory overlay and integrate it with the existing ADS tree logic.

What would be the recommended approach to implement such a solution? Or is there a practical workaround we could use?

[absolute0kelvin]

Yes. Using SeqAds needs maintaining a copy of the data files. An alternative solution is possible but we have not working on it. If you can help designing a solution we'll be very thankful.