SSDs Have Become Fast, Except in the Cloud

Re:SSDs Have Become Fast, Except in the Cloud by scottlamb on Tuesday February 20, 2024 @02:16PM (#39445578)

Interesting. I worked at Google until January 2021. I see 2019 dates on that PDF, but I wasn't aware of snap when I left. There was some alternate RPC approach (Pony Express, maybe? I get the names mixed up) that claimed 10 µs or so but was advertised as experimental (iirc had some bad failure modes at the time in practice) and was simply unavailable in many of the datacenters I needed to deploy in. Maybe they're two names for the same thing. [edit: oh, yes, starting to actually read the paper now, and: "Through Snap, we created a new communication stack called Pony Express that implements a custom reliable transport and communications API."]

Actual latency with standard Stubby-over-TCP and warmed channels...it's been a while, so I don't remember the number I observed, but I remember it wasn't that much better than 0.5 ms. It was still bad enough that I didn't want to add a tier that would have helped with isolation in a particularly high-reliability system.

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Re:SSDs Have Become Fast, Except in the Cloud by kccqzy on Tuesday February 20, 2024 @03:51PM (#39446740)

Snap was the external name for the internal project known as User Space Packet Service (abbreviated USPS) so naturally they renamed it prior to publication. I deployed an app using Pony Express in 2023 and it was available in the majority of cells worldwide. Pony Express supported more than just RPC though. The alternate RPC approach that you spoke of was called Void. It had been experimental for a long time and indeed it wasn't well known even inside Google.

> but I remember it wasn't that much better than 0.5 ms.

If you and I still worked at Google I'd just give you an automon dashboard link showing latency an order of magnitude better than that to prove myself…

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Re:SSDs Have Become Fast, Except in the Cloud by scottlamb on Tuesday February 20, 2024 @04:33PM (#39447211)

Interesting, thanks!

> If you and I still worked at Google I'd just give you an automon dashboard link showing latency an order of magnitude better than that to prove myself…

I believe you, and I think in principle we should all be getting the 50 µs latency you're describing within a datacenter with no special effort.

...but it doesn't match what I observed, and I'm not sure why. Maybe difference of a couple years. Maybe I was checking somewhere with older equipment, or some important config difference in our tests. And obviously my memory's a bit fuzzy by now but I know I didn't like the result I got.

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