Feature request: expose a metric for series-per-metric

[bboreham]

Is your feature request related to a problem? Please describe.

Tenants have no visibility how close they are to the max-series-per-metric limit. The limit applies to an internal count which is incremented when a series is created and decremented when it is removed by garbage-collection after head compaction (i.e. every 2 hours).

Describe the solution you'd like

At least a metric per tenant showing the largest single count. Perhaps an upgrade to the cardinality api to show these counts.

Describe alternatives you've considered

count(metric) does not account for the 2-hour retention. Maybe some sort of count_over_time computation would approximate it, but I can't find one.

[wilfriedroset]

Totally agreed for exposing this information into the cardinality api. This would help tenants better understand their usage