[Salgat]

We use something similar for our event based databases. We project millions of events into an in-memory object (usually a dictionary), and periodically persist that state as json in S3. It's guaranteed to be consistent across all service instances because the persisted state contains the event stream positions to catchup from. The only drawback of course is that it can use up to several GB of memory depending on how big the state is, but it's extremely fast and doing in-memory operations is trivial compared to using SQL or a library with api calls.