NOTE
Guava RateLimiter
Local token/rate limiting with Guava RateLimiter and its limits in distributed systems.
This is a historical learning note and may contain outdated or incomplete understanding.
Guava RateLimiter controls the average rate at which permits are granted in one process. Callers acquire one or more permits and may wait depending on the API/policy.
It is useful for local smoothing/protection, but it is not a distributed global rate limit. Multiple application instances each have independent state unless an external coordination design is added.
A rate limit also needs overload semantics: wait, reject, shed, or degrade. Bound waiting by request deadlines so rate limiting does not merely convert overload into excessive latency.