Error opening connection to database / database \"postgres_exporter\" does not exist

What did you do?

• Deployed postgres_exporter via ansible-role prometheus.prometheus.postgres_exporter
• Preparations following the wonderful documentation https://github.com/prometheus-community/postgres_exporter#running-as-non-superuser
• Service unit postgres_exporter.service failed (logs see below)
• Problem identified and fixed local (see below)

What did you expect to see?

It would have been great if the README https://github.com/prometheus-community/postgres_exporter#running-as-non-superuser had included the following SQL query.

 CREATE DATABASE postgres_exporter;

That solved the issue.

What did you see instead? Under which circumstances?

The monitoring system and metrics reported downtime for the PostgreSQL server.

Environment

• System information:

  Linux 6.12.94+deb13-amd64 x86_64

• postgres_exporter version:

  0.20.1

• postgres_exporter flags:

  • database
  • replication_slot
  • stat_bgwriter

• PostgreSQL version:

  17

• Logs:

journalctl -u postgres_exporter.service -e

relevant output:

Aug 12 06:54:17 social postgres_exporter[686468]: time=2026-08-12T06:54:17.300Z level=ERROR source=collector.go:191 msg="Error opening connection to database" err="error querying postgresql version: pq: database \"postgres_exporter\" does not exist"
Aug 12 06:54:18 social postgres_exporter[686468]: time=2026-08-12T06:54:18.300Z level=ERROR source=postgres_exporter.go:606 msg="error scraping dsn" err="Error opening connection to database (postgresql://postgres_exporter:PASSWORD_REMOVED@localhost:5432/?sslmode=disable): pq: database \"postgres_exporter\" does not exist" dsn="postgresql://postgres_exporter:PASSWORD_REMOVED@localhost:5432/?sslmode=disable"

Open the README section on running as a non-superuser and compare its setup steps with the reported failure. Document the CREATE DATABASE postgres_exporter statement, then verify the rendered README clearly explains that the database must exist before starting postgres_exporter.