## Problem
Original Slack discussion:
https://neondb.slack.com/archives/C04DGM6SMTM/p1739915430147169
TL;DR in Postgres, it's totally normal to have 'invalid' DBs (state
after the interrupted `DROP DATABASE`). Yet, some of our metrics
collected with `sql_exporter` try to get the size of such invalid DBs.
Typical log lines:
```
time=2025-03-05T16:30:32.368Z level=ERROR source=promhttp.go:52 msg="Error gathering metrics" error="[from Gatherer #1] [collector=neon_collector,query=pg_stats_userdb] pq: [NEON_SMGR] [reqid 0] could not read db size of db 173228 from page server at lsn 0/44A0E8C0"
time=2025-03-05T16:30:32.369Z level=ERROR source=promhttp.go:52 msg="Error gathering metrics" error="[from Gatherer #1] [collector=neon_collector,query=db_total_size] pq: [NEON_SMGR] [reqid 0] could not read db size of db 173228 from page server at lsn 0/44A0E8C0"
```
## Summary of changes
Ignore invalid DBs in these two metrics -- `pg_stats_userdb` and
`db_total_size`
4b77807de9