type allTierStats struct {
	Tiers map[string]tierStats `msg:"ts"`
}

func newAllTierStats() *allTierStats {
	return &allTierStats{
		Tiers: make(map[string]tierStats),
	}
}

func (ats *allTierStats) addSizes(tiers map[string]tierStats) {
	for tier, st := range tiers {
		ats.Tiers[tier] = ats.Tiers[tier].add(st)
	}
}

func (ats *allTierStats) merge(other *allTierStats) {
	for tier, st := range other.Tiers {