WARNING: Active Record does not support composite primary key

Summary

During work on a ticket (internal link) relating to project import/export, the customer noticed new warnings at GitLab 13.6 importing the project using the Rails console:

TABLE has composite primary key. Composite primary key is ignored.
WARNING: Active Record does not support composite primary key.

These new warnings were also noticed in our test logs etc. A summary of internal discussion(s) on Slack:

• A number of tables had primary keys added, for example !45198 (merged)
• The tables had unique composite keys before, but they were not marked as primary. These composite keys were promoted.
• This is to fix an issue relating to replication; turning on logical replication breaks without a primary key.
• The warning comes from ActiveRecord
• At this time, while the warnings are annoying, but no functionality is thought to be affected.

The purpose of this issue is to make a publicly searchable record of this warning in the issue tracker. Setting it low priority and severity: the warnings may get suppressed at some point.

Steps to reproduce

Example Project

What is the current bug behavior?

What is the expected correct behavior?

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes