# Linking Metrics to Traces — OpenTelemetry

Source: https://www.skillbyai.com/en/opentelemetry/m-exemplars

> Exemplars and RED from spans.

## From a spike to an example trace

**Exemplars** attach a sample trace ID to metric data points, for example to a histogram bucket, so a dashboard can link a latency spike directly to a trace that experienced it. Backends such as Prometheus (with exemplar storage enabled) and Grafana support them. Another approach derives metrics from spans: the Collector's **spanmetrics connector** produces request rate, error and duration metrics from traces, giving RED metrics even where no metrics are instrumented.

## Generating RED metrics from spans in the Collector

A connector links a traces pipeline to a metrics pipeline (contrib distribution).

```yaml
connectors:
  spanmetrics:
    histogram:
      explicit:
        buckets: [50ms, 100ms, 250ms, 500ms, 1s, 2s]

service:
  pipelines:
    traces:
      receivers: [otlp]
      processors: [batch]
      exporters: [otlp/tempo, spanmetrics]     # the connector acts as an exporter here
    metrics:
      receivers: [spanmetrics]                 # ...and as a receiver here
      processors: [batch]
      exporters: [prometheusremotewrite]
```

## Mind sampling when deriving metrics

Metrics computed from sampled traces undercount unless they are generated before sampling.

**Quiz:** What is an exemplar?

- [ ] A metric type
- [x] A sample trace ID attached to a metric data point
- [ ] A log level
- [ ] A sampling policy

*Answer:* A sample trace ID attached to a metric data point. Links metrics to traces.