Transactions. It's relatively easy to atomically edit random data in a file on disk, if you're willing to overwrite the entire file with your new version. But a

Transactions. It's relatively easy to atomically edit random data in a file on disk, if you're willing to overwrite the entire file with your new version. But as soon as you need to edit files that are too big for that approach, the problem becomes exceptionally complicated. Indexing any columns you want in one line of code is also very nice.