That's an apples to oranges comparison though. Upstash couples durability with consistency/isolation. Regardless of configuration, FaunaDB and DynamoDB both always ensure durability of acknowledged writes with a fault tolerance of greater than 1 node failure. To compare them on equal footing, Upstash would need to be configured for strong consistency, at least according to the docs.
It does. The three AZs they replicate across are just as good as anything else someone typically calls a "datacenter." Amazon itself operates retail out of one region and uses multi-AZ as a fault tolerance strategy.
It won’t lose data in the event of a data center failure. Each of the replicas is in a different AZ, and at least two of three have to durably write the data before the put succeeds.
In my code, Upstash database was eventually consistent. Similarly the index in the FaunaDB was not serialized.
But both of those should not affect the latency numbers in the histogram because those numbers are all read latency.