Avoid having a large backlog of messages with the same message group ID in Amazon SQS

For FIFO queues, there can be a maximum of 20,000 in flight messages (received from a queue by a consumer, but not yet deleted from the queue). If you reach this quota, Amazon SQS returns no error messages. A FIFO queue looks through the first 20k messages to determine available message groups. This means that if you have a backlog of messages in a single message group, you can't consume messages from other message groups that were sent to the queue at a later time until you successfully consume the messages from the backlog.

Note

A backlog of messages that have the same message group ID might build up because of a consumer that can't successfully process a message. Message processing issues can occur because of an issue with the content of a message or because of a technical issue with the consumer.

To move away messages that can't be processed repeatedly, and to unblock the processing of other messages that have the same message group ID, consider setting up a dead-letter queue policy.