Why should you care?

ShopNest cannot lose or double-apply order_placed under retries.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

// Outbox row: Id, Type, Payload, CreatedAt, ProcessedAt
Console.WriteLine("RELAY: SELECT TOP pending FOR UPDATE SKIP LOCKED");
Console.WriteLine("RELAY: publish bus");
Console.WriteLine("RELAY: mark ProcessedAt");
Console.WriteLine("CONSUMER: idempotent upsert by EventId");

What happened?

• This deepens the basic outbox lesson with relay concurrency and consumer idempotency.
• SKIP LOCKED style claiming avoids double publish races.

Practice next

1. Add ProcessedAt to outbox.
2. Relay marks processed only after broker ack.
3. Consumer stores seen EventIds.
4. Exponential retry on publish fail.
5. Dead-letter poison payloads.

Remember

Claim → publish → mark. At-least-once everywhere. Idempotent consumers.

ShopNest outbox relay

Worker publishes pending outbox with leases.

Outcome: Events survive app crashes after commit.