Can you explain the concept of Transactional Outbox and why it is used?

Transactional Outbox is a pattern used to ensure reliable message delivery in distributed systems, especially when it is necessary to guarantee consistency between the database and the messaging system.

The idea is that when performing a business operation that changes data, a special record (outbox) with information about the event to be published is written within the same transaction.

After a successful transaction commit, a separate process or service reads these records from the outbox and sends messages to a queue or message broker.

This helps avoid issues with message loss or data desynchronization, as the record in the outbox and the data change occur atomically.

Example:

1. In a transaction, we update the orders table and add a record to the outbox table.
2. After commit, a separate worker reads new records from the outbox and publishes events to Kafka, RabbitMQ, etc.
3. After successful sending, the record from the outbox is deleted or marked as processed.

This approach ensures reliable integration between the database and the messaging system without data loss.