How to destroy millions of dependent objects in Rails

Question

In Rails I have always used dependent: :destroy to remove dependent objects.

However in the following scenario it doesn't work properly because Subscriptions and Notifications are very large, with millions of objects that must be destroyed.

Users --> Projects  --> Subscriptions
                   \
                    --> Notifications

Some problems are:

• the deletion is very slow and can take many hours (I could use a background job)
• I cannot use dependent: :delete_all on large tables because it would block the database for a long time
• user.destroy wraps all the deletions inside a transaction (I don't think it's good for a database which must serve other queries in the meantime)

What is the Rails way to handle a large destroy with millions of records? Are there any gems that can help and handle the dependent: :destroy in a better way (e.g. outside a transaction)? What approach would you suggest in this case?

Answer 1

Starting from Rails 6.1 it's possible to do dependent: :destroy_async to destroy associations in the background

 has_many :subscriptions, dependent: :destroy_async

just posted this for future reference