[name] asked: Why did we need the Transaction Outbox?

Transaction Outbox is a pattern used to ensure reliable delivery of messages or events from a database to other systems.

Why it is needed:

• When an application modifies data in the database and simultaneously needs to send an event (for example, to a message queue), it is important that these two operations are atomic — either both happen or neither.
• Since database transactions and external systems (queues, services) cannot be combined into a single transaction, there is a risk of desynchronization.

Transaction Outbox solves this problem as follows:

1. Within a single transaction, the main change is written to the database along with a record in a special Outbox table containing event data.
2. After commit, a separate process reads records from the Outbox and sends them to the target system (e.g., Kafka, RabbitMQ).
3. After successful sending, the record from the Outbox is deleted or marked as sent.

Thus, reliable delivery of events is achieved without loss or duplication, which is critical for systems with integration and analytics.