Saga Pattern: An Example

Placing an order touches four services. Stock is reserved, the card is charged, a shipment is booked, and the order is confirmed. Each of those writes to a different database.

One database transaction could cover all four. Four databases cannot. A saga is what replaces it.

The Shape

A saga is a sequence of local transactions. Each one commits on its own, in its own service, and each one has a compensation that undoes it.

There is no rollback. Once a step has committed, the only way back is to run another transaction that reverses the effect