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Metrics, Logs and Traces
Three complementary signals.
What each signal answers
Metrics are numbers sampled over time (requests per second, error ratio, memory used): cheap to store, fast to query and ideal for dashboards and alerts. Logs are detailed event records that explain what happened in a specific case. Traces follow one request across services to show where time was spent. Prometheus focuses on metrics; Grafana can display all three when connected to tools such as Loki (logs) and Tempo (traces).
Numbers over time
Prometheus pulls numeric measurements from your services and stores them as labelled time series.
A car dashboard, a logbook and a GPS track
The speedometer (metrics) tells you something is wrong at a glance, the logbook (logs) records each event in detail, and the GPS track (traces) shows the exact route a single trip took.
Alert on metrics, debug with logs and traces
Metrics detect problems cheaply; logs and traces explain them.
त्वरित जाँच: Which signal is best for cheap, fast alerting on error rates?
- Traces only
- Logs only
- Metrics
- Screenshots
Answer
Metrics — Aggregated numbers are cheap to evaluate.