implement a simple database filter for user queries

[WnP]

Port code from https://github.com/prometheus-community/postgres_exporter/compare/master...pvanderlinden:databases-filter?expand=1

Fixes #443 Tested and works as expected.

[splitt3r]

This looks promising 👍🏻 Great work

[ilanKeshet]

What is preventing this PR from being merged?

[sebglon]

Can we have a feedback on this MR? Why is it not merged? @SuperQ or @sysadmind

[WnP]

feature branch has been rebased onto master @sysadmind :heavy_check_mark:

[nvx]

Anything blocking this from being merged?

[zachfeld]

@WnP This looks great - excited to see it merged! Can you share an example of what the config would look like for user queries running on specific databases?

[WnP]

@WnP This looks great - excited to see it merged! Can you share an example of what the config would look like for user queries running on specific databases?

@zachfeld you'll be able to use something like the following in your query.yaml:

prod_total_users:
  query: "SELECT count(*) as nb_users from users"
  master: true
  databases: "prod.*"
  metrics:
    - nb_users:
      usage: "GAUGE"
      description: "Total number of users."

where databases is a valid golang regular expression.

[SuperQ]

User extended queries are now deprecated.