Postgres Size Metric requires CONNECT permissions to all Databases

[Setheck]

Description

The Postgres size metric seems to run the following query
"SELECT pg_database.datname, pg_database_size(pg_database.datname) as size_bytes FROM pg_database" seen (

prometheus/postgres.go

Line 207 in 54c3070

rows, err := p.DB.Raw("SELECT pg_database.datname, pg_database_size(pg_database.datname) as size_bytes FROM pg_database").Rows()

)

This query fails with the following on AWS RDS
ERROR: permission denied for database rdsadmin

This is because it would require CONNECT permissions to all database to get the size with pg_database_size

When metrics are collected they should only reference the current database.

Is there any reason not to change this to be something like
SELECT current_database() as datname, pg_database_size(current_database()) size_bytes;
?