I'll also add that if it's a case that doesn't require more than one process writing simultaneously, sqlite really shines. I know that's probably not satisfying in a thread that starts as "i want fs transactions" - but it's a solid consolation prize.

they've put a lot of effort into making it work well even in likely-to-crash situations (e.g., running on a phone with a user who doesn't tend to the battery)

https://www.sqlite.org/fasterthanfs.html

https://www.sqlite.org/atomiccommit.html

https://www.sqlite.org/hirely.html