pg_stat_activity_count only reporting 1. Config issue?

[wtip]

I have the exporter running but my pg_stat_activity_count is only reporting 1 connection which is not accurate. I'm running the exporter as non-superuser and followed the permissions queries. Other metrics are working fine but I guess it's not getting access to pg_stat_activity.
What queries could I run to verify that I've set the permissions properly?

postgres=# \z postgres_exporter.pg_stat_activity
                                             Access privileges
      Schema       |       Name       | Type |      Access privileges       | Column privileges | Policies
-------------------+------------------+------+------------------------------+-------------------+----------
 postgres_exporter | pg_stat_activity | view | postgres=arwdDxt/postgres   +|                   |
                   |                  |      | postgres_exporter=r/postgres |                   |
(1 row)

postgres=# \dn
            List of schemas
       Name        |       Owner
-------------------+-------------------
 postgres_exporter | postgres_exporter
 public            | postgres

postgres=# \dv postgres_exporter.pg_stat_activity
                   List of relations
      Schema       |       Name       | Type |  Owner
-------------------+------------------+------+----------
 postgres_exporter | pg_stat_activity | view | postgres

[wtip]

I've had the same results on a postres 9.2 and 9.5 server

[johto]

Answering here since I happened to be on IRC where this was discussed. From #103:

In PostgreSQL, views run as the defining user, meaning you don't
need a view wrapping a function (you can just have a view). This
improves readability, maintainability, performance, and clarity.

This is not true. The permissions checks for views are done from the point of view of the owner, but the actual execution happens under the user that executed the query. The most obvious case where this matters is when a view calls a function; the function is NOT executed as the owner of the view. pg_stat_activity is such a view, as it calls pg_stat_get_activity().

(The view approach might appear to work on 9.6 and later due to a change in 9.6: "Use the privilege system to manage access to sensitive functions." I'm not sure.)

[wrouesnel]

I think I'm going to mark this one help wanted since done documentation updates are needed. But what I'd really like is an obvious test case to ensure non-superuser permissions work.

Adding an endpoint which dumps the correct config based on connection string I think would resolve the ambiguity.

[Fra-nk]

After doing a little research:

(The view approach might appear to work on 9.6 and later due to a change in 9.6: "Use the privilege system to manage access to sensitive functions." I'm not sure.)

https://www.postgresql.org/docs/current/static/default-roles.html implies this will work with Postgres 10 if you execute

GRANT pg_monitor TO postgres_exporter;

While Postgres <= 9.6 requires the old mechanism

CREATE FUNCTION postgres_exporter.f_select_pg_stat_activity()
RETURNS setof pg_catalog.pg_stat_activity
LANGUAGE sql
SECURITY DEFINER
...