* drops by RATE_REFILL every second. If the counter is below RATE_CREDIT
* then the request is processed; otherwise it is processed with probability
* 1/(counter - RATE_CREDIT).
* drops by RATE_REFILL every second. If the counter is below RATE_CREDIT
* then the request is processed; otherwise it is processed with probability
* 1/(counter - RATE_CREDIT).