Dual-write problem.

also: dual write · dual-write · dual writes · dual-writes

Writing to two systems (the database and a message broker) in one operation without atomicity, so a crash can leave them disagreeing.

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Save the order, then publish OrderCreated: the process can crash between the two.
Result: an order with no event, or an event for an order that rolled back.
2PC across a database and Kafka is not an option (Kafka doesn't support XA).
Fix: write once (DB + outbox in one transaction) and derive the event from it.

also: dual write · dual-write · dual writes · dual-writes

Writing to two systems (the database and a message broker) in one operation without atomicity, so a crash can leave them disagreeing.

Save the order, then publish OrderCreated: the process can crash between the two.
Result: an order with no event, or an event for an order that rolled back.
2PC across a database and Kafka is not an option (Kafka doesn't support XA).
Fix: write once (DB + outbox in one transaction) and derive the event from it.