# The Data Model — Prometheus + Grafana

Source: https://www.skillbyai.com/en/prometheus-grafana/f-model

> Metric names, labels and samples.

## A series is a name plus labels

Every time series is identified by a **metric name** and a set of **labels** (key-value pairs), for example `http_requests_total{method="GET", route="/api/orders", status="200"}`. Each sample is a float value with a timestamp. Prometheus adds target labels such as `job` and `instance` at scrape time. Each unique combination of label values is a separate series, which is why labels must have a limited set of values. The exposition format is plain text.

## What a /metrics endpoint returns

The text exposition format (illustrative values).

```text
# HELP http_requests_total Total HTTP requests handled.
# TYPE http_requests_total counter
http_requests_total{method="GET",route="/api/orders",status="200"} 10432
http_requests_total{method="GET",route="/api/orders",status="500"} 17
http_requests_total{method="POST",route="/api/orders",status="201"} 2210
# HELP process_resident_memory_bytes Resident memory size in bytes.
# TYPE process_resident_memory_bytes gauge
process_resident_memory_bytes 5.2346e+07
```

## Follow naming conventions

Use snake_case, a unit suffix (_seconds, _bytes) and _total for counters, as the Prometheus naming guide recommends.

**Quiz:** What identifies a unique time series in Prometheus?

- [ ] The value
- [ ] The metric name only
- [ ] The scrape timestamp
- [x] The metric name together with its full set of label values

*Answer:* The metric name together with its full set of label values. Each label combination is a series.