db.go
func (seq *Sequence) Next() (uint64, error) {
	seq.Lock()
	defer seq.Unlock()
	if seq.next >= seq.leased {
		if err := seq.updateLease(); err != nil {
			return 0, err
		}
	}
	val := seq.next
	seq.next++
	return val, nil
}
func (seq *Sequence) Next() (uint64, error) {
	seq.Lock()
	defer seq.Unlock()
	if seq.next >= seq.leased {
		if err := seq.updateLease(); err != nil {
			return 0, err
		}
	}
	val := seq.next
	seq.next++
	return val, nil
}
// Next would return the next integer in the sequence, updating the lease by running a transaction
// if needed.