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

[pedrovinicius]

I'm using this gem in production alongside with Sinatra, ActiveRecord 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')

database_connections.each do |connection_info|
  connection = ActiveRecord::Base.establish_connection(connection_info)
  connection.execute('SELECT * FROM ...')
  # Other SQL queries here
  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?

[rowland]

It would be easier if you were using ActiveRecord OR fb, rather than something in between. If you're not making use of ActiveRecord, either connect directly using fb's API or grab raw_connection from ActiveRecord::Base.connection.

fb's connection's execute method either returns a cursor or takes a block with a cursor as a parameter. Basically, you need to program against the API as it exists, and not how you're guessing it is.

If you just want results, raw_connection.query will give you them. Given that execute returns a cursor, you should close that cursor when you're done iterating it.