Kafka Quota机制

计算限流时间（throttleTime）的逻辑：
O * W / (W + X) = T => X = (O - T)/T * W
O：实际速率（10M/s）
T：目标速率 （1M/s）
W：窗口时间 （10s）
X：延迟时间 （9s）

/*

• This calculates the amount of time needed to bring the metric within quota
• assuming that no new metrics are recorded.
• Basically, if O is the observed rate and T is the target rate over a window of W, to bring O down to T,
• we need to add a delay of X to W such that O * W / (W + X) = T.
• Solving for X, we get X = (O - T)/T * W.
  */
  private def throttleTime(clientMetric: KafkaMetric, config: MetricConfig): Int = {
  val rateMetric: Rate = measurableAsRate(clientMetric.metricName(), clientMetric.measurable())
  val quota = config.quota()
  val difference = clientMetric.value() - quota.bound
  // Use the precise window used by the rate calculation
  val throttleTimeMs = difference / quota.bound * rateMetric.windowSize(config, time.milliseconds())
  throttleTimeMs.round.toInt
  }