code: func SampleSize(s int) TracerOption {
  	if s <= 0 {
  		panic("sample size must be greater than 0")
  	}
  	return func(o *tracerOptions) *tracerOptions {
  		o.sampleSize = s
  		return o
  	}
  }
docs: // SampleSize sets the number of requests between two adjustments of the sampling
  // rate when MaxSamplingRate is set. Defaults to 1,000.