Sagas

Definition

A saga [3] is a sequence of atomic transactions T ₁,...,T _n for which the following execution guarantee is made. Either the component transactions T _i will all commit in the order

$$T_1 \,T_2,..., T_n$$

in which case that saga is said to have committed, or one of the transaction sequences

$$T_1,...,T_j \,C_j, ...,C_1$$

will be executed (for some 0 ≤ j < n), in which case the saga is said to have aborted. The transactions C _i are compensating transactions for the corresponding saga transactions T _i . Each transaction T _i in a saga must have a corresponding compensating transaction, which is responsible for undoing the T _i ’s effects.

Key Points

A saga is a type of extended transaction model [1] Each component transaction in a saga is executed atomically, but the saga itself is not atomic. Effects of the component transactions are visible to other operations as soon as those transactions commit, which may be well before the saga has finished.

The saga model guarantees...