Contradictory information is given about how many levels of priority are supported by Quorum Queues - 2 or 4?

[oliverlockwood]

Describe the bug

According to https://www.rabbitmq.com/docs/priority#declaration:

Classic queues support priorities in the [0, 255] range. Quorum queues support a much smaller range: 1 through 4.

According to https://www.rabbitmq.com/docs/quorum-queues#priorities:

Quorum queues internally only support two priorities: high and normal. Messages without a priority set will be mapped to normal as will priorities 0 - 4. Messages with a priority higher than 4 will be mapped to high.

Which of these statements is accurate?
Given we are in the process of migrating classic queues to quorum queues, it's rather important for us to know the answer...!

Many thanks.

Reproduction steps

Read two different sections of the RabbitMQ documentation.

Expected behavior

The documentation should be internally consistent.

Additional context

No response

[michaelklishin]

@oliverlockwood quorum queues in 4.2 support two priorities (normal for the priorities in the [0; 4] range, higher for [5; ∞]).

The source of confusion comes from the fact that classic queues implement priorities very differently and require the maximum number to be specified upfront.

I will edit the docs but as the Priority Queues guide explains, priorities only avoid the head-of-queue blocking problem, so no one really needs 10 or 20 priorities, "normal" and "high" is enough.
And quorum queues give you just that without any application modifications.

That said, as of RabbitMQ 4.3 quorum queues will support up to 32 priorities. Not that it would make any practical difference, we do it mostly because with an upcoming new major Raft implementation version and another QQ revision, we'd be able to do it and it looks closer to how CQs expose priorities.

[michaelklishin]

e965344 updates a couple of relevant guides.

[oliverlockwood]

@michaelklishin thank you for taking the time to update this documentation so promptly. It is now much clearer to me.