max_ready

Specifies the maximum number of messages that can be in the ready queue. The ready queue is the set of messages that are immediately eligible for delivery.

If a message is promoted from its delayed queue to the ready queue and it would take the size of the ready queue above max_ready, the message will be delayed by a randomized interval of up to 60 seconds and placed back into the scheduled queue before being considered again.

Moving a message from ready to scheduled as a result of hitting this limit may trigger disk IO to save the content of the message if the message was received with deferred spooling enabled. In addition, other in-memory state is discarded to reduce memory utilization, and it will need to be re-loaded from the spool when the message is tried again later.

The default for max_ready is 1024 messages.

Raising the limit will increase RAM utilization in exchange for decreasing the IO load to your spool storage.