code: func (e *RuntimeStatsColl) GetCopStats(planID string) *CopRuntimeStats {
  	e.mu.Lock()
  	defer e.mu.Unlock()
  	copStats, ok := e.copStats[planID]
  	if !ok {
  		copStats = &CopRuntimeStats{stats: make(map[string][]*RuntimeStats)}
  		e.copStats[planID] = copStats
  	}
  	return copStats
  }
docs: // GetCopStats gets the CopRuntimeStats specified by planID.