Comment by blakepelton | Hacker News Reader

Comment by blakepelton | Hacker News Reader

Parent Full thread

Some recent academic work suggests implementing caches directly in network switches. Tofino switches are programmable enough that academics can implement this today.

OrbitCache is one example, described in this paper: https://www.usenix.org/system/files/nsdi25-kim.pdf

It should solve the thundering herd problem, because the switch would "know" what outstanding cache misses it has pending, and the switch would park subsequent requests for the same key in switch memory until the reply comes back from the backend server. This has an advantage compared to a multi-threaded CPU-based cache, because it avoids performance overheads associated with multiple threads having to synchronize with each other to realize they are about to start a stampede.

A summary of OrbitCache will be published to my blog tomorrow. Here is a "draft link": https://danglingpointers.substack.com/p/4967f39c-7d6b-4486-a...

> This has an advantage compared to a multi-threaded CPU-based cache, because it avoids performance overheads associated with multiple threads having to synchronize with each other to realize they are about to start a stampede.

The switch presumably also has multiple cores which still need to do this work, no? Or is the claim that moving this synchronization to the router behind a network hop saves CPU cycles on the app server?

The relevant part of the switch hardware described by the OrbitCache paper doesn't have typical processor cores. Instead it is an "RMT" pipeline.

I wrote a brief description of RMT here: https://danglingpointers.substack.com/p/scaling-ip-lookup-to...

That's not completely unheard of. Cavium used to sell chips intended to go in switches and routers which had a sort of programmable hash function that could be applied to incoming packets, and then use the result of that hash to route the packets.

These days you'd have to assume someone somewhere has a neural net based router.

This sounds intriguing and terrible at the same time :D

Reply on news.ycombinator.com