code: func RunUnbuffered(c context.Context, root *ds.Key, fn func(context.Context) ([]Mutation, error)) error {
  	cfg := getConfig(c)
  	shardSet, _, _, err := enterTransactionInternal(c, cfg, root, fn, 0)
  	if err != nil {
  		return err
  	}
  	fireTasks(c, cfg, shardSet, true)
  	return nil
  }
docs: // RunUnbuffered opens a lightweight unbuffered transaction on "root"
  // runs "fn" inside of it. Any mutations returned by "fn" will be registered
  // at the end of the transaction if "fn" doesn't return an error.
  //
  // This is useful as an initial starting point without incurring any of the
  // overhead of spinning up a new buffered transaction.
  //
  // During "fn"'s execution, standard Tumble operations such as PutNamedMutation
  // and CancelNamedMutation may be performed.