Cardinality as Observability's Resource Constraint¶

The number of unique dimension combinations (cardinality) determines storage and query costs exponentially; high-cardinality fields make metrics systems economically infeasible.

Tension Addressed¶

Detail vs. Noise - cardinality is the mechanism by which detail creates cost

Recognizable As¶

Any labeling/tagging system where dimension combinations create unique series; decisions about "what to include in tags/labels"; query costs growing faster than data volume

Canonical Sources¶

Prometheus documentation on cardinality; Google SRE Book metrics chapters

Transfers To¶

Database indexing (multi-column index combinatorics), Data warehousing (dimension explosion), Feature engineering (curse of dimensionality)

Cardinality explosion occurs when dimensions like user_id or request_id are included in metrics - unique combinations grow multiplicatively. The solution is always structural: high-cardinality data belongs in logs/traces, not metrics.