There are many occasions when we need to group queues based on the priority like critical queue should be consumed first then low priority queues. Rqueue supports two types of priority

1. Weighted
2. Strict

You need to set priorityMode in container factory either STRICT or WEIGHTED.

Priority needs to be specified using RqueueListener annotation’s field priority. Multiple queues can be grouped together using priorityGroup field, by default any queue having priority is added to the default priority group. Queue can be classified into multiple priority groups as well for example sms queue has 4 types of sub queues critical, high, medium and low their priority needs to be specified as priority="critical=10, high=6, medium=4,low=1".

If you want to use simple priority mechanism, then you need to set priority to some number and their group, for example.

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

Let’s say there’re three queues

Queue	Priority
Q1	6
Q2	4
Q3	2

Weighted Priority

Weighted priority works in round-robin fashion, in this example Q1 would be polled 6 times, Q2 4 times and Q3 2 times and again this process repeats. After polling if it’s found that any queue does not have more jobs than their weight is reduced by Δ e.g Q1 does not have any item then it’s weight is reduces by Δ = currentWeight * (1-(6/(6+4+2)). As soon as the weight becomes <= 0, queue is inactive and weight is reinitialised when all queues become inactive.

This algorithm is implemented in WeightedPriorityPoller

Strict Priority

In Strict priority case, poller would always first poll from the highest priority queue, that’s Q1 here. After polling if it encounters that if queue does not have any element than that queue becomes inactive for polling interval, to avoid starvation a queue can be inactive for maximum of 1 minute.

This algorithm is implemented in StrictPriorityPoller

Additional Configuration

• rqueue.add.default.queue.with.queue.level.priority: This flags controls whether the default queue should be added in the listeners where priority has been defined like priority="critical=5,high=3", if we add then the such queues will have one additional level that would be the default one, the default value is true.
• rqueue.default.queue.with.queue.level.priority: The priority of the default queue, when rqueue.add.default.queue.with.queue.level.priority is true, by default queue is placed in the middle.