This post illustrates the difference between persistence and a database. If you are expecting to simply persist one instance of one application's state across

This post illustrates the difference between persistence and a database. If you are expecting to simply persist one instance of one application's state across different runs and failures, a database can be frustrating. But if you want to manage your data across different versions of an app, different apps accessing the same data, or concurrent access, then a database will save you a lot of headaches. The trick is knowing which one you want. Persistence is tempting, so a lot of people fool themselves into going that direction, and it can be pretty painful. I like to say that rollback is the killer feature of SQL. A single request fails (e.g. unique violation), and the overall app keeps going, handling other requests. You application code can be pretty bad, and you can still have a good service. That's why PHP was awesome despite being bad -- SQL made it good (except for all the security pitfalls of PHP, which the DB couldn't help with).