Wildcard support for topic metrics

[vkuznecovas]

What would you like to be added or enhanced?

The metrics endpoint for topics should allow for specifying wildcards in the topic.

Why is this needed?

If you use EMQX subscriptions with wildcards and have a whole bunch of topics (50k+ for, example) it is not currently possible to get any relevant metrics metrics for such a subscription.

I'd like to see the message rates for such subscriptions so that I can automatically scale my subscribers in a k8s install.

[kjellwinblad]

Thanks for an interesting feature request.

An idea: Create a "dummy" rule without any action and use a a rule SQL that looks something like this:

SELECT * FROM "my_interesting_topic_pattern/#"

Now, you should be able to use the rule metrics to get some information about how many messages matches the topic pattern. Is this an acceptable solution?