Understanding the Saga Pattern for Distributed Transactions in Microservices

The two‑phase commit is a classic way to ensure atomicity across multiple entities, but in a microservices architecture each service has its own database, making traditional ACID transactions impractical.

To maintain consistency, distributed transactions are required; the Saga pattern, first described in 1987, provides a practical solution by chaining local transactions across services.

Saga can be implemented via two main approaches: Event/Choreography, where services emit and listen to events without a central coordinator, and Command/Orchestration, where a coordinator directs the sequence of local transactions.

In the choreography example, an order service creates an order and publishes ORDER_CREATED_EVENT ; the payment service reacts, charges the customer, and emits BILLED_ORDER_EVENT ; the stock service updates inventory and emits ORDER_PREPARED_EVENT ; the delivery service ships the product and publishes ORDER_DELIVERED_EVENT ; finally the order service marks the order as completed.

Rollback in a Saga is not free; compensating actions such as refunding the payment and marking the order as failed are required when a later service (e.g., stock) cannot complete its step.

Key advantages of the choreography style are simplicity and loose coupling, while its disadvantages include difficulty scaling beyond a few steps, potential circular dependencies, and testing challenges.

Images illustrating the high‑level microservice architecture and the step‑by‑step saga flow are included in the original article.