What does generally cause the "Dropped db cursor" error?

[pedrovinicius]

I'm using this gem in production alongside with Sinatra and Puma. Puma is running with 2 workers.

My code for database queries is identical to the following snippet:

database_connections =  YAML.load_file('./databases_list.yml')

def iterate_over_servers(&block)
  database_connections.each do |conection_info|
    conn = ActiveRecord::Base.establish_connection(connection_info)

    yield conn
  end
end

iterate_over_servers do |connection|
  Person.where(name: '', email: '') #...
  connection.disconnect!
end

I have a list of identical databases (running on distinct servers) that I have to connect to and collect some data. But I'm suspecting I'm doing something terribly wrong, as when this code gets executed, the ruby interpreter raises a Dropped DB Cursor exception.

Do you have any idea of what can be possibly causing this error?