in appender.go [258:266]
func (a *Appender) addCount(delta int64, lm *int64, m metric.Int64Counter, opts ...metric.AddOption) {
// legacy metric
if lm != nil {
atomic.AddInt64(lm, delta)
}
attrs := metric.WithAttributeSet(a.config.MetricAttributes)
m.Add(context.Background(), delta, append(opts, attrs)...)
}