We do have an abstract db layer which is used by various pieces of the wallet backend. It is currently implemented through mutable shared variables (MVar) which lives in-memory and don't get persisted. Working towards a minimal-viable-solution, we need data to actually get serialized, persisted and deserialized such that they can survive a restart. We are going for a simple SQLite implementation in this first iteration which will likely be sufficient for quite a long time in the future as well, even for big players like exchanges.