Dead letter queue

In message queueing a dead letter queue (DLQ) is a service implementation to store messages that the messaging system cannot or should not deliver.[1] Although implementation-specific, messages can be routed to the DLQ for the following reasons:

  1. The message is sent to a queue that does not exist.[2][3]
  2. The maximum queue length is exceeded.
  3. The message exceeds the size limit.
  4. The message expires because it reached the TTL (time to live)[4]
  5. The message is rejected by another queue exchange.[5]
  6. The message has been read and rejected too many times.[6]

Routing these messages to a dead letter queue enables analysis of common fault patterns and potential software problems.[7] If a message consumer receives a message that it considers invalid, it can instead forward it an Invalid Message Channel,[8] allowing a separation between application-level faults and delivery failures.

Queueing systems that incorporate dead letter queues include Amazon EventBridge,[9] Amazon Simple Queue Service,[7] Apache ActiveMQ, Google Cloud Pub/Sub,[10] HornetQ, Microsoft Message Queuing,[2] Microsoft Azure Event Grid and Azure Service Bus,[11] WebSphere MQ,[12] Solace PubSub+,[13] Rabbit MQ,[5] Apache Kafka[14] and Apache Pulsar.[15][16]

See also

References
  1. "Dead Letter Channel". www.enterpriseintegrationpatterns.com.
  2. Redkar, Arohi (2004). Pro MSMQ: Microsoft Message Queue Programming. Apress. p. 148. ISBN 1430207329.
  3. "Dead-letter queues". IBM. Retrieved 23 February 2014.
  4. "Dead Letter Exchanges — RabbitMQ". www.rabbitmq.com. Retrieved 2020-12-06.
  5. RabbitMQ dead letter queue "Dead Letter Exchanges".
  6. "Amazon SQS dead-letter queues". AWS.
  7. "Using Amazon SQS Dead Letter Queues". Amazon. Retrieved 23 February 2014.
  8. "Invalid Message Channel". www.enterpriseintegrationpatterns.com.
  9. "Amazon EventBridge announces support for Dead Letter Queues". Amazon.
  10. "Forwarding to dead-letter topics | Cloud Pub/Sub". Google Cloud. Retrieved 2020-12-26.
  11. spelluru. "Compare Azure messaging services". docs.microsoft.com. Retrieved 2020-01-17.
  12. Böhm-Mäder, Johannes (14 December 2011). WebSphere MQ Security: Tales of Scowling Wolves Among Unglamorous Sheep. BoD. p. 68. ISBN 978-3842381506.
  13. "Solace Dead Message Queues".
  14. "Apache Kafka documentation".
  15. "Apache Pulsar documentation".
  16. "Apache Pulsar PIP-22:Dead Letter Topic". GitHub.
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