A distributed transaction manager is responsible for coordinating transactions across multiple resources or databases within a distributed system. Its primary role is to ensure that all parts of a transaction either commit successfully or roll back entirely, thereby maintaining data consistency and integrity across different systems. This is essential in scenarios where an application needs to perform operations that affect multiple databases or services, such as in microservices architectures or when integrating with third-party APIs.
The distributed transaction manager uses protocols like the Two-Phase Commit (2PC) to achieve this coordination. In the first phase, it communicates with all participating resources to gather their preparedness to commit to the transaction. This involves each resource locking the necessary data and sending a response back to the manager. If all responses are affirmative, the manager then initiates the second phase, instructing each resource to commit the transaction. If any resource indicates a failure or the manager itself encounters an issue, it will initiate a rollback, ensuring that no partial changes are made across the involved systems.
In practice, consider an online retail application where a user places an order. This transaction might involve the inventory database to reserve stock, the payment gateway to process payment, and the shipping service to arrange delivery. If the payment is successful but the inventory cannot confirm the stock due to a system failure, the distributed transaction manager will ensure that the payment is reverted, preventing any inconsistencies. Thus, the distributed transaction manager acts as a critical component for managing complex interactions in distributed environments, enhancing reliability and reducing the risk of data inconsistencies.