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).
I'd say the universal query capability is the killer feature of SQL.
In the OP they spent two weeks designing and implementing transaction-save indexes -- something that all major SQL RDBMS (and even many NoSQL solutions) have out of the box.
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).