> Does any developer here on HN really believe that JSON parsing (plus schema validation) is what adds the most latency to a request? It just doesn't add up that just switching to PB would deliver that speedup.
I've absolutely had times when json serialising/deserialising was the vast majority of the request time.
100%. In fact, I've usually found in my career that serialization/deserialization is the largest latency contributor, except when the API call makes remote database requests or something equally expensive. For the critical path of, say, game state updates, it's best to keep as much as you can in-memory on-box, so ridiculously expensive operations like json deserialization really stand out by comparison. Even for enterprise web crud calls, it's quite important when you're part of a giant ensemble of web calls, some of which may be serially dependent, to worry about things like this.
I've absolutely had times when json serialising/deserialising was the vast majority of the request time.