What happens when a queue has no consumers?

If a queue has no active consumers, messages simply keep accumulating in it - they are not lost, as long as the queue itself still exists.

What happens next depends on the queue's configuration:

• A normal durable queue just grows, consuming more memory and disk over time.
• An auto-delete queue is only removed once it has had at least one consumer that later disconnects - a queue that never had a consumer is not auto-deleted.
• If x-max-length or a similar limit is set, older messages start getting dropped or dead-lettered once the limit is reached.
• If x-message-ttl is set, individual messages expire and are removed or dead-lettered after their TTL passes.

Unbounded growth with no consumers is a common cause of the memory/disk alarms that trigger RabbitMQ's flow control.

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