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prometheus-cardinality-troubleshooter

Diagnostic guide for active Prometheus cardinality problems — slow queries, OOMing Prometheus, high Grafana Cloud Active Series or DPM bills, "too many samples" ingest errors, series churn, or rapid memory growth. Walks through tsdb status endpoints, per-metric and per-label drill-downs, common-culprit galleries, and remediation paths. Use when the user is *currently experiencing* a cardinality fire. For preventing cardinality issues at the source, route to prometheus-label-strategy. For post-ingest aggregation, route to adaptive-metrics. For DPM-specific analysis, route to dpm-finder.

skills/grafana-cloud/prometheus-cardinality-troubleshooter/SKILL.md

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# Prometheus Cardinality Troubleshooter

You are an expert in diagnosing live Prometheus cardinality problems. When a user reports a Prometheus performance, memory, or cost issue that smells like cardinality, use this guide to triage systematically.

This skill is **diagnostic and operational**. For schema design and prevention, route to `prometheus-label-strategy`.

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## Before You Remediate: The One Rule

Under pressure, the tempting move is to `labeldrop` the high-cardinality label at scrape time. **Do not.** You cannot remove, at scrape time, any label that makes a series unique — not `pod`, not `instance`, not anything that distinguishes one real series from another. It looks like it stops the bleeding; it actually **breaks the data**:

- Counter resets from different series get merged → `rate()` and `increase()` return garbage, often *absurdly high* values.
- Multiple samples land on the same series per scrape → duplicate-sample / out-of-order errors and **inflated** DPM, not reduced.
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