Priority queue

There is often a need when messages with higher importance should be given priority in processing compared to general messages with lower priority. This pattern is important for applications that provide different service level agreements (SLA) to consumers, which provide services based on different plans and subscriptions.

Queues follow first-in, first-out patterns. Messages are processed in sequence. However, with the help of this pattern, it is possible to fast-track processing of certain messages due to their higher priority. There are multiple ways to implement it. If the queue provides the capability of assigning priority and based on priority re-order messages, then even a single queue is enough to implement this pattern.

However, if the queue does not have the capability to re-order messages, then separate queues can be created for different priorities and each queue can have separate consumers associated with it.

In fact, this pattern can reuse competing consumer patterns if needed to fast-track processing of messages from each queue using multiple consumers.