Rails can easily serve up pages in <100ms. If you do have an endpoint that is CPU-bound to where you can’t meet your SLA goals, you can serve up just that endpo

Rails can easily serve up pages in <100ms. If you do have an endpoint that is CPU-bound to where you can’t meet your SLA goals, you can serve up just that endpoint in Rust or Golang. But that’s rare. Usually what happens at scale is that the SQL database starts slowing down as more data is loaded in. Partitioning, indexes and painful refactorings aren’t prioritized. Engineering will champion “a faster language”—that incidentally allows them a new data model where they add in proper indexes at the start. They aren’t really incentivized to realize they could see the same gains by just improving their existing data inside the Rails monolith. Source: experience improving performance (including latency) with multi-billion-dollar Rails monoliths