Cardinality is now a metric. dash0.metrics.timeseries reports your distinct series count as a time series, so it works anywhere a metric works: a dashboard panel, a PromQL query, an alert check. dash0.metrics.timeseries is synthetic, computed from metric data you already sent, so there is nothing to turn on and no extra charge. Like every synthetic metric it carries no attributes of its own. You pick the dimensions by grouping in PromQL (or via the Query Builder):
1topk(10, sum by (otel_metric_name) ({otel_metric_name="dash0.metrics.timeseries"} offset 5m))
That gives you your ten largest metrics by series count.
otel_metric_name appears twice, and that is deliberate. The first matcher selects the synthetic metric. The second filters the data points underneath by their own metric name, so you can pin a single metric:
1sum({otel_metric_name="dash0.metrics.timeseries", otel_metric_name="k8s.container.ready"} offset 5m)
Use an offset between five and ten minutes. Dash0 syncs the underlying metric metadata with a short delay, and without the offset the last few minutes of the chart trail off toward zero.
Grouping by a resource attribute answers the other question, where the series come from rather than which metric they belong to. sum by (k8s_namespace_name) finds the namespace, sum by (service_name) finds the service.
More information
- The metric registry has the full definition
- Understand Synthetic Metrics covers how synthetic metrics are queried.