We use an event database (think Kafka) as our source of truth and we've largely shifted away from redis and elasticsearch in favor of local in-memory singletons. These get pretty big too, up to 6GB in some cases for a single mapping. Since it's all event based data, we can serialize the entire thing to json asynchronously along with the stream event numbers specific to that state and save the file to s3. On startup we can restore the state for all instances and catchup on the remaining few events. The best part is that the devs love being able to just use LINQ on all their "database" queries. We do however have to sometimes write these mappings to be lean to fit in memory for tens of millions of entries, such as only one property we use for a query, then we do a GET on the full object in elasticsearch.