Dead-letter queue
Holds messages that repeatedly fail processing so they stop blocking the main queue.
Problem it solves: Poison messages otherwise retry forever.
Where it sits: Side output of a consumer.
When to use
- Any queue consumer with retries.
When not to use
- As a place to forget about failures — alert on it.
Failure modes
- Unmonitored DLQ silently loses business events.
Metrics to watch
- DLQ depth
- Redrive rate
Alternatives
- Parking-lot table
Configuration in Labs (illustrative defaults)
- Queue capacity (messages) = 1000000 — Messages the queue can hold. Beyond this, new messages are rejected (dropped).