mvcc/backend/batch_tx.go
func (t *batchTx) UnsafeForEach(bucketName []byte, visitor func(k, v []byte) error) error {
	return unsafeForEach(t.tx, bucketName, visitor)
}
func (t *batchTx) UnsafeForEach(bucketName []byte, visitor func(k, v []byte) error) error {
	return unsafeForEach(t.tx, bucketName, visitor)
}
// UnsafeForEach must be called holding the lock on the tx.