The concept of overdrafting is a combination of modern business rule and ancient technological limitation (dating back to before-computers when accounting was manual and checks and checkbooks were also big deal, which his hella-eventually consistent). It can still serve as a useful metaphor, regardless.
But if you care about operating the EXCHANGE ITSELF then your allusion to the audit trail is a bit of a red herring, isn't it? In fact, the data store itself becomes pretty irrelevant for the live trade-matching - presumably you shard just the hell out of your data, keep the working set in RAM, keep most of your stuff colocated in the same place and just solve for availability by doing something crazy and hardware-intensive like having hot spares for everything.
But if you care about operating the EXCHANGE ITSELF then your allusion to the audit trail is a bit of a red herring, isn't it? In fact, the data store itself becomes pretty irrelevant for the live trade-matching - presumably you shard just the hell out of your data, keep the working set in RAM, keep most of your stuff colocated in the same place and just solve for availability by doing something crazy and hardware-intensive like having hot spares for everything.