Avoid comment calls in pg:dump

[jaynetics]

Summary

This causes lines like COMMENT ON EXTENSION plpgsql IS 'PL/pgSQL procedural language'; to no longer appear in the db:structure:dump when using PostgreSQL.

Such comment calls don't seem to add a lot of value.

They are bad, however, because with them, db:structure:load only works for db superusers, as described in #36816, which is hard to debug due to the generic error ActiveRecord::StatementInvalid: PG::InsufficientPrivilege: ERROR: must be owner of extension.

[ghiculescu]

@jaynetics thanks for the PR. There was a recent discussion about this in #43107 where @eileencodes pointed out that this is pretty easy to fix without framework changes.

I'll leave this open for now, but just wanted to share some context in case it doesn't get much traction.

[jaynetics]

@ghiculescu thanks for the input.

i agree that it is easy to fix once you know what the problem is. just finding out the problem is a bit hard based on the given error message.

in my opinion, it would be best if the structure stuff just works in most normal scenarios, and does not rely on some of the users googling error messages.

if you agree, i'd do some more work on this to make it apply only to PostgreSQL >= 11 as described in #43107.

otherwise, at least the error message should be improved in my opinion.

[ghiculescu]

@jaynetics I'm not on the core team so don't take this as an endorsement either way, but I personally would like to see this in Rails. Just don't want to get your hopes up too much if it doesn't happen!

Making it work with Postgres 11 is definitely needed, it'd look something like this:

rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

Line 184 in 78e4020

database_version >= 110_000

This also needs a CHANGELOG entry.

[jaynetics]

@ghiculescu i've added the version check and changelog entry.

[ghiculescu]

heads up - this was reverted in #44633