parallel_migration_threads of anything greater than 1 raises ActiveRecord::ConcurrentMigrationError

[jwg2s]

Steps to reproduce

• Set config.parallel_migration_threads = 4 (really anything greater than 1 will expose the issue)
• Run bundle exec rake db:migrate

Expected behavior

• All schemas should be migrated without error

Actual behavior

• ActiveRecord::ConcurrentMigrationError error is raised, migrations fail.

  
  ActiveRecord::ConcurrentMigrationError:

Cannot run migrations because another migration process is currently running.

## System configuration

<!-- Please let us know as far as you can. -->

* Database: Postgres v14.12

* Apartment version: Happens regardless of `ros-apartment` version, but confirmed on `3.1.0` and `2.11.0`

* Apartment config (in `config/initializers/apartment.rb` or so):

  * `use_schemas`: `true`
  * `parallel_migration_threads`: `4`

* Rails (or ActiveRecord) version: `6.1.7.9`

* Ruby version: `3.1.4`

[mnovelo]

@jwg2s I need to update our README that parallel migrations won't work unless you implement your own schema-aware advisory locks for migrations. I'm seeking advise for how to advise users who want to use parallel migrations https://github.com/rails/rails/pull/43500#issuecomment-2447817077

[mnovelo]

@jwg2s try disabling advisory_locks as noted here https://blog.saeloun.com/2019/09/09/rails-6-disable-advisory-locks/

[jwg2s]

Thanks, @mnovelo - that worked locally so we're unblocked on at least playing around with it. Curious - do you have a functional example of schema-aware advisory locks anywhere?

[mnovelo]

Glad that worked for y'all, at least locally @jwg2s .

I do not have a functional example of schema-aware advisory locks. IMHO, I don't think they're any safer than removing advisory locks completely, so they're not worth implementing. If someone else does, I'd be happy to include it in a wiki or in the README.

I'll mark this issue as closed for now.