Relevant telegraf.conf:

[[inputs.postgresql_extensible]]
address = "database=foo"
databases = ["foo"]
[[inputs.postgresql_extensible.query]]
sqlquery = "select 1"

System info:

ba1484c

Docker

Steps to reproduce:

1. Run the above configuration

Expected behavior:

A metric should be emitted with the tag db=foo

Actual behavior:

The metric is emitted with the tag db=postgres

Additional info:

Apparently postgres is a hard-coded value when the statement you are executing does not return a datname field.
This is wrong by all accounts as neither the db in the connection string, nor the db in the database list is postgres. In addition, this behavior (of relying on the datname column) is completely undocumented, and I had to go digging through the source to find out what was going on.

https://github.com/influxdata/telegraf/blob/ba1484c/plugins/inputs/postgresql_extensible/postgresql_extensible.go#L267-L283