Looks very much like, at 3k req/s, that request was cached somewhere (either disk/memory/proxy), which are exactly the kind of optimizations the user mentioned

Looks very much like, at 3k req/s, that request was cached somewhere (either disk/memory/proxy), which are exactly the kind of optimizations the user mentioned you need to think about. Given that you do need to tell Rails when to cache, it may be trivial, but you're still thinking about it.