Update puma.rb generator template to reconcile with Puma documentation

[zach-taylor]

Summary

I'm attempting to reconcile some documentation on ActiveRecord connections between Puma's README and the default generated Puma config file in Rails.

What's recommended in the Puma README:

on_worker_boot do
  ActiveSupport.on_load(:active_record) do
    ActiveRecord::Base.establish_connection
  end
end

What's in the default puma.rb:

on_worker_boot do
  ActiveRecord::Base.establish_connection if defined?(ActiveRecord)
end

Other Information

The config was originally added by @schneems here: #23057

Not sure if he had some reasoning behind not using ActiveSupport.on_load (perhaps ActiveRecord will always already be loaded by this point?)

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[schneems]

Is there a reason to use "on_load"? What does it buy us?

[zach-taylor]

@schneems after some additional research, I think the whole point of preloading an application is to load your application once (including ActiveRecord::Base) and use CoW to create the workers. Therefore ActiveRecord::Base should always already be loaded at this point (if you're using ActiveRecord) and this change doesn't make sense.

I think I will open a pull request to Puma instead. Appreciate the time, thanks!

[matthewd]

Does #28057 render all the current explicit-connection-management advice irrelevant?