In Rails, do I need to worry about failed transactions if the same model gets updated by two different mongrels?

Question

I have a fairly vanilla rails app with low traffic at present, and everything seems to work OK.

However, I don't know much about the rails internals and I'm wondering what happens in a busy site if two requests come in at the same time and try to update the same model, from (I assume) two separate mongrel processes. Could this result in a failed transaction exception or similar, or does rails do any magic to serialize controller methods?

If an update could fail, what is the best practice to watch for and handle this type of situation?

For more background, my controller methods often update multiple models. I currently don't do anything special to create transactions and just rely on the default behaviors. Ideally I'd like the update to be retried rather than return an error (the updates are generally idempotent, i.e. doing them twice if necessary would be OK). My database is mysql.

Answer 1

afaik, mysql will wait until the first transaction is processed and then it will process the second one. #create, #update and #save get their stuff wrapped in an SQL transaction. And I guess mysql can handle those well.