mysql insert race condition

Question

How do you stop race conditions in MySQL? the problem at hand is caused by a simple algorithm:

1. select a row from table
2. if it doesn\'t exist, insert it

Answer 1

On a technical level, a transaction will help here because other threads won't see the new row until you commit the transaction.

But in practice that doesn't solve the problem - it only moves it. Your application now needs to check whether the commit fails and decide what to do. I would normally have it rollback what you did, and restart the transaction because now the row will be visible. This is how transaction-based programmer is supposed to work.