Does it feel wrong to access memory synchronously? It all depends on the i/o operation, where and for how long it's blocking. Nostrdb should be crazy fast, way faster than sqlite3 whose most popular bindings are...also sync. Sync allows for API design that async does not, and I want that flexibility at this lower level. You can always turn sync into async but not the other way round.

I am very confused on what you are calling sync. Sync I/O is not the same as promises/futures that you mentioned before. Regarless, any Lmdb-based citrine-like option can reach similar performance levels as an embed lmdb option because the cost of communication is negligible compared to the I/O.