# Choose request metrics for external monitoring

Choose a measurement by the question it answers. `system.processes` describes requests active now; `system.query_log` describes recorded request events. Coordinator DB does not document a Prometheus metrics endpoint or a built-in mapping from every query counter to a metric name.

```sql
SELECT count(*) AS active_requests,
       max(elapsed) AS oldest_elapsed_seconds
FROM system.processes;
```

The observing request may appear in this snapshot. Do not interpret that count as a perfectly independent external connection count.

For completed work, aggregate terminal history within the observation period your collector manages. Avoid counting both start and finish events as separate executed queries. Distinguish `QueryFinish` from the two exception event types, and account for any configured minimum logging duration.

Use units in any externally chosen metric names. Durations in query history are milliseconds, `elapsed` in active requests is seconds, and memory counters are bytes. Terminal peak memory is a per-request peak, so summing it does not report current server memory. A monitoring collector must also handle repeated observations without double counting events.

See [process counters](https://coordinatordb.com/docs/reference/system-tables/processes), [query history](https://coordinatordb.com/docs/reference/system-tables/query-log) and [logging settings](https://coordinatordb.com/docs/reference/settings/session-settings/log-queries).