4.0: Remove classic queue mirroring

[dcorbacho]

Quorum queues and streams are now the only replicated data structures. Classic queues
are still around as a non-replicated type.

Types of Changes

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)
• Build system and/or CI

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• I have added tests that prove my fix is effective or that my feature works
• All tests pass locally with my changes
• If relevant, I have added necessary documentation to https://github.com/rabbitmq/rabbitmq-website
• If relevant, I have added this change to the first version(s) in release-notes that I expect to introduce it

[ansd]

It looks like consumer argument x-cancel-on-ha-failover should have been deleted as part of this PR.

Likewise, MQTT connections don't need to perform failover for mirrored classic queues in

rabbitmq-server/deps/rabbitmq_mqtt/src/rabbit_mqtt_processor.erl

Lines 2000 to 2004 in c67c940

	%% Consuming classic queue is down.
	%% Let's try to re-consume: HA failover for classic mirrored queues.
	case consume(Q, QoS, State0) of
	{ok, State} ->
	State;

anymore.

[michaelklishin]

Filed #11540 for those two.

[michaelklishin]

It is not entirely obvious to me, what the rabbit_channel of x-cancel-on-ha-failover should do now: always recover? For classic (no longer replicated) queues the choice is less obvious.

[ansd]

Copied from internal Slack:

Channels should not try to re-register consumers.
If the classic queue is down, consumption is stopped and the client gets notified.
Likewise, MQTT connection should not try to re-consume. Instead, the MQTT connection will be terminated.
I think it would be less confusing just to always cancel the consumer