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You need to know the number of network threads and the order in which the listeners are declared in the brokers' server.properties to properly aggregate per protocol.We

On the broker side only - where multiple security protocol can coexist - 
we should add a tag showing the listener label, that would also make it much easier to group the metrics in a tool like Grafana.

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• What impact (if any) will there be on existing users?
  
  Users currently using reporters that do not support metric tags and flatten the tags map into the metrics name, will find that the name has changed
• The socket-server-metrics.* are not exposed as Yammer metrics which are still the most commonly consumed server-side metrics, so the impact of this change is mitigated (thanks Ismael Juma Juma)

Rejected Alternatives