Comment by hansvm

The system is free to commit immediately after a write() -- fsync or closing the file simply guarantees commits.

>Based on your scenario, if an application-level "change" involves updating 2 files

It could be two parts of the same file too. E.g. if you're using a single file with something like recutils with a single file to implement double-entry accounting and only commit one entry. You'll at least be able to detect the corruption in that case (not that you can in general), but you won't be able to fix it using only the contents of the file.