What is the Saga pattern, how does it work, and what is it used for?

The Saga pattern is an architectural approach for managing distributed transactions in microservices, where traditional ACID transactions are impossible or undesirable.

How it works:

• A saga consists of a sequence of local transactions across different services.
• Each local transaction has a compensating operation (rollback).
• If one of the transactions fails, compensating transactions are triggered to undo the already completed steps, restoring the system to a consistent state.

Purpose:

• Ensures data consistency in distributed systems without locking.
• Allows handling errors and rollbacks at the business logic level.

Example: when placing an order, the item is first reserved, then the money is deducted. If the money deduction fails, a compensating transaction is executed — canceling the item reservation.

In Java, this can be implemented using an orchestrator (a central controller) or choreography (events between services).