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

• 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 rails/rails#43500 (comment)

[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.