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Comment by evanweaver | Hacker News Reader

Your own docs say that by default “writes are not guaranteed to be durable even if the client receives a success response”.

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Upstash has two consistency modes. Eventual consistency and Strong consistency. Please see: https://docs.upstash.com/overall/consistency

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.

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.

DynamoDB also guarantees your write is distributed to multiple data centers as well.

No it doesn't. The write is not durable in other datacenters when the client acknowledgement is returned. It is still possible to lose data.

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.

An AZ is not a datacenter.

This is what I was referring to: An Availability Zone (AZ) is one or more discrete data centers with redundant power, networking, and connectivity in an AWS Region. AZs give customers the ability to operate production applications and databases that are more highly available, fault tolerant, and scalable than would be possible from a single data center. All AZs in an AWS Region are interconnected with high-bandwidth, low-latency networking, over fully redundant, dedicated metro fiber providing high-throughput, low-latency networking between AZs. All traffic between AZs is encrypted. The network performance is sufficient to accomplish synchronous replication between AZs. AZs make partitioning applications for high availability easy. If an application is partitioned across AZs, companies are better isolated and protected from issues such as power outages, lightning strikes, tornadoes, earthquakes, and more. AZs are physically separated by a meaningful distance, many kilometers, from any other AZ, although all are within 100 km (60 miles) of each other.

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.

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