[o11c]

This is a reminder that "we want to support bursts" is much more common thing than "we want a higher ratelimit". Often multiple levels of bursts are reasonable (e.g. support 10 requests per minute, but only 100 requests per day; support 10 requests per user, but only 100 requests across all users).

There are several ways to track history with just a couple variables (or, if you do have the history, but only accessing a couple of variables); the key observation is that you usually don't have to be exact, only put a bound on it.

For history approximations in general, one thing I'm generally fond of is using an exponential moving average (often with λ=1/8 so it can be done with shifts `ema -= ema>>3; ema += datum>>3` and it's obvious overflow can't happen). You do have to be careful that you aren't getting hyperbolic behavior though; I'm not sure I would use this for a rate limiter in particular.