ActiveRecord execute SQL need to close connection? DEPRECATION WARNING: Database connections will not be closed automatically

Question

First off, I am using Rails 3.2 on Puma (but with MRI), and am not doing any explicit threading by hand.

I am in places using the execute method, like MyModel.connection.execute or I know ActiveRecord::Base.connection.execute can do the same thing since all connections are to the same DB for me right now.

I recently started seeing

DEPRECATION WARNING: Database connections will not be closed automatically, please close your database connection at the end of the thread by calling `close` on your connection. For example ActiveRecord::Base.connection.close

This seems self-explanatory, but I can find very little information on it online, mostly about using ActiveRecord with Sinatra (ex ActiveRecord connection warning. (Database connections will not be closed automatically)).

I read this:

http://blog.daniel-azuma.com/archives/216

which suggests that Rack middleware does it for me as long as the DB execute transaction is done in a controller (if I understand correctly). Does this mean transactions done elsewhere (such as a model, or decorator - they're useful in many places, so I don't want to put them right in a single controller) must be explicitly closed? Even if it's a model method that does it which was called from a controller, ex:

class MyController
  def show
    MyModel.do_execute_sql_stuff
  end
end

class MyModel
  def self.do_execute_sql_stuff
    connection.execute("WHATEVER;")
  end
end

Do I need to explicitly close here? If so, should I use MyModel.connection.close or MyModel.clear_active_connections! as the article suggests? Maybe because English is not my first language, but that method sounds dangerous! And how do I go do it?

conn = MyModel.connection
result = conn.execute("STUFF")
do_stuff_with(result)
conn.close |or| MyModel.clear_active_connections!

Like that?

What about when using find_by_sql? Will it return the connection to the pool, or do I have to explicitly do that?

EDIT: Strangely, I only see this in my production logs. Not on development, nor staging (which should be identical to production).

Answer 1

In This case You need to close your connection manually.

After running your script, you can close it Manually like this.

after do
  ActiveRecord::Base.connection.close
end