Metric cardinality.
also: high cardinality · label cardinality · cardinality explosionThe number of distinct label combinations a metric has; unbounded labels such as user_id explode storage and cost.
the two-minute refresher
- Safe labels are bounded: method (about 10), status (about 20), endpoint (about 100), service.
- Never label by user_id, request_id or email: millions of time series.
- Put high-cardinality detail in logs and traces instead.