code: func (agg *HealthD) purge() {
  	var threshold = agg.intervalDuration * 5 // NOTE: this is arbitrary.
  	for k, _ := range agg.hostAggregations {
  		if time.Since(k.Time) > threshold {
  			delete(agg.hostAggregations, k)
  		}
  	}
  
  	n := len(agg.intervalAggregations)
  	if n > agg.maxIntervals {
  		agg.intervalAggregations = agg.intervalAggregations[(n - agg.maxIntervals):]
  	}
  }
docs: // purge purges old hostAggregations older than 5 intervals