func (seq *Sequence) Release() error {
	seq.Lock()
	defer seq.Unlock()
	err := seq.db.Update(func(txn *Txn) error {
		var buf [8]byte
		binary.BigEndian.PutUint64(buf[:], seq.next)
		return txn.Set(seq.key, buf[:])
	})
	if err != nil {
		return err
	}
	seq.leased = seq.next
	return nil
}
func (seq *Sequence) Release() error {
	seq.Lock()
	defer seq.Unlock()
	err := seq.db.Update(func(txn *Txn) error {
		var buf [8]byte
		binary.BigEndian.PutUint64(buf[:], seq.next)
		return txn.Set(seq.key, buf[:])
	})
	if err != nil {
		return err
	}
	seq.leased = seq.next
	return nil
}
// Release the leased sequence to avoid wasted integers. This should be done right
// before closing the associated DB. However it is valid to use the sequence after
// it was released, causing a new lease with full bandwidth.