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6.2The Three Pillars Compared
| Pillar | What It Captures | Best For | Cardinality | Storage Cost |
|---|---|---|---|---|
| Logs | Discrete events with context | Debugging specific incidents | High (one per event) | High |
| Metrics | Aggregated numerical measurements | Alerting, dashboards, trends | Low (pre-aggregated) | Low |
| Traces | Request flow across services | Understanding distributed behavior | Medium (sampled) | Medium |
Metrics are the first line of defense: they tell you something is wrong. Traces tell you where. Logs tell you why.