Rails 3 locking auction engine tables

Question

I am creating an auction system in Rails 3 (using PostgreSQL as a database).

Imagine you have a Product. The product has many offers.

I’m worried about what happens when two different users click “Bid” at the same time (assuming I have at least 2 application servers and they get to the servers at the same time). I have two possible acceptable behaviors for this:

• one of them wins and the other receives an error message
• one of them “wins”, and the other bid is created next (each bet adds 0.01 euros to the price). Thus, all simultaneous bets are repeated until they are created

So my question is: how to deal with this problem on Rails 3? I think using regular transactions is not enough or is it?

Answer 1

Rails pessimistic locking should allow you to achieve what you want. As far as I know, this will allow you to handle the issue of ordering updates in the database without errors.

Here is a thread that better explains two different types of blocking: Optimistic and pessimistic blocking