Logs, metrics and traces
Choose the evidence that contains the fact, and count the series your metric attributes create.
Predict first
Before you read: predict
A catalog incident has six recent request outcomes. The local export groups them into error=2 and ok=4, contains a trace tree with four child-to-parent links, and one rejection event body.
Which record lets on-call compare the error outcomes before choosing a request to inspect?
The 30-second version
Metrics aggregate measurements; logs record events; traces connect spans belonging to an operation. Start with the record that answers the present question, then move to a related record when the question changes. Metric dimensions affect how many series are stored, while detailed evidence can retain identifiers outside the metric. S1
Choose the evidence that contains the fact, and count the series your metric attributes create.
How it works
Step 1 of 6
Analogy: Apiary inspection records
Imagine an invented record system with a site summary, an inspection notebook and a linked checklist for each visit. The summary reveals how many visits reported a problem. A checklist shows which activities belonged to one visit. The notebook records what someone observed during an activity. Looking at more summary totals cannot recover a sentence that was never included there.
| Record | Signal role |
|---|---|
| Summary grouped by site and outcome | Metric series |
| Individual observation note | Log event |
| Linked activities in one inspection | Trace and spans |
| Visit reference on a note | Correlation identifier |
This is a recordkeeping analogy, not a claim about beekeeping practice. A trace represents instrumented work, not necessarily every activity. A log is not inherently an explanation; it helps only when useful information was recorded. Trace relationships also do not establish that a particular operation caused a failure. S3 S4
Metrics are convenient for trends and alert conditions because many observations can collapse into a compact aggregate. That advantage depends on dimensions. Every distinct label combination creates another time series in the Prometheus model, with storage, memory and processing costs. A unique request identifier can defeat the intended aggregation. The fixture demonstrates series growth; it does not measure a vendor bill or establish a universal price ordering. S2 S5
Logs and traces can retain individual identifiers without making those identifiers metric dimensions. They still have collection and storage costs; more detail is not free. Choose fields for a concrete diagnostic question and apply the system's data-handling policy. The useful workflow is to move from an aggregate symptom to a relevant operation and then to its event details, checking correlation rather than assuming adjacent records belong together. This is a workflow, not a rule that every investigation must start from an alert. S3 S4
Try it
Answer first, then check. Nothing is saved.
Question 1 of 4
An alert tells a catalog team that recent outcomes changed. The export holds a metric, a trace and a log for the same requests.
Which one can reconstruct the operations that participated in one selected request?
Question 2 of 4
A catalog investigator must account for a rejected price. The export holds a metric, a trace and a log for that request.
Which one carries the recorded rejection reason?
Question 3 of 4
A single catalog route produces eight metric series. The same export also contains one route-only series and a request trace.
Which instrumentation choice can account for the eight metric series?
Question 4 of 4
Five catalog quotes are rejected, each inside its own catalog.quote span. The instrumentation calls counter.add(1, {route: '/quote'}) and logger.emit({body: 'quote rejected'}), passing the root context instead of the span's context.
What does the export report as [metric series, rejection events joined to their span]?
Go deeper
Pro tip
Use one quantity and unit consistently in a metric name; a name should not mix incompatible meanings. This naming habit makes later dashboards easier to interpret. Prometheus naming guidance, read 2026-09-29.
Sources
Fetched and read 2026-09-30. Own sources/ files preserve extracted text with URL, date and SHA256 headers. No verbatim source quotations are used in graded items; their outcomes are executed.
- S1: OpenTelemetry authors, Signals.
- S2: OpenTelemetry authors, Metrics.
- S3: OpenTelemetry authors, Logs.
- S4: OpenTelemetry authors, Traces.
- S5: Prometheus authors, Metric and label naming.
- S6: OpenTelemetry authors, JavaScript instrumentation.
Checked against the tools and docs as of 2026-09-29.