Glossary term
What is Cardinality? Meaning for developers
In System Design
Number of unique label combinations in metrics. Example: Adding user_id as a label creates millions of series.
Learn it properly · System DesignLesson 46: Logs, Metrics & Traces: The Three Pillars“Checkout took 20 seconds and failed” — but checkout touches eleven components. How logs, metrics and traces each answer a different question, how to instrument with OpenTelemetry, and how linking them takes you from “something's wrong” to “here's why” in minutes.In Observability & SRE
How many different values a label can take, or how many time series a metric creates.
Learn it properly · Observability & SRELesson 2: Metrics and Prometheus: Counters, Gauges, Histograms and PercentilesThe metric types, labels and cardinality, why averages lie, percentiles, and a real Prometheus scrape of a Node service.