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You could easily observe this with a cache-cold query performing lots of random IO. EBS latency is on the order of milliseconds, even cheap baremetal nowadays is microseconds

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Also rds caps out around 20k IOPS. You can hit 1 million IOPS on a large machine with a bunch of SSDs. Imagine running 50 rds databases instead of 1.

It's a huge bummer that EBS is the only durable block storage in aws since the performance is so bad. Has anyone had luck using instance storage? The aws white papers make it seem like you could lose data there for any number of reasons, but the performance is so much better. Maybe a synchronous replica in a different AZ?

I've used Aurora and the IO is much better there than on vanilla RDS. Postgres Aurora is basically a fork of postgres with a totally different storage system. Their are some neat re:Invent talks on it if you are interested.

We use aurora actually. It's a lot more scalable, but also pretty expensive. The IO layer is multi-tenent, and unfortunately when it goes wrong, you have no idea why and no recourse. I think I've never had a positive experience with AWS support about it either. We've had IO latency go from <2ms to >10ms and completely destroy throughput. Support tells us to try optimizing our queries like we are idiots.

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