There are situations where queues need to be grouped based on priority, ensuring critical tasks are handled before lower priority ones. Rqueue provides two types of priority handling:

Weighted: Allows specifying different numeric priorities for queues. Strict: Enforces strict ordering of queues based on priority. To configure priority handling in Rqueue:

Set priorityMode in the container factory to either STRICT or WEIGHTED. Use the priority field in the RqueueListener annotation to assign priorities to individual queues. Use the priorityGroup field to group multiple queues together. By default, any queue with a specified priority is added to the default priority group. You can categorize queues into multiple priority groups. For instance, a SMS queue might have sub-queues like critical, high, medium, and low, with priorities specified as priority=”critical=10, high=6, medium=4, low=1”. If you prefer a simpler priority mechanism, assign a numeric priority directly to each queue and its group. For example:

priority="60" priorityGroup="critical-group"

Let’s say there’re three queues

Weighted Priority

Weighted priority operates in a round-robin manner, where each queue’s polling frequency is determined by its assigned weight. In this example, Q1 is polled 6 times, Q2 4 times, and Q3 2 times before the cycle repeats. If a queue is found to have no items during polling, its weight is reduced by Δ. For instance, if Q1 has no items, its weight decreases by Δ = currentWeight * (1 - (6 / (6 + 4 + 2))). When a queue’s weight drops to or below 0, it becomes inactive. The weights are reinitialized when all queues are inactive.

This algorithm is implemented in WeightedPriorityPoller

Strict Priority

In strict priority mode, the poller always starts by polling from the highest priority queue, which is Q1 in this case. After polling, if the queue is found to have no elements, it becomes inactive for a designated polling interval. To prevent starvation, a queue can remain inactive for a maximum of 1 minute before becoming eligible for polling again.

This algorithm is implemented in StrictPriorityPoller

Additional Configuration

• rqueue.add.default.queue.with.queue.level.priority: This flag determines whether the default queue should be added to listeners where a priority has been defined using priority="critical=5,high=3". If enabled (true), such queues will include an additional default level. The default value for this flag is true.

• rqueue.default.queue.with.queue.level.priority: This setting specifies the priority of the default queue when rqueue.add.default.queue.with.queue.level.priority is set to true. By default, the queue is positioned in the middle of the defined priority levels.

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