> OK, interesting, I think I see... So you are asking about if SQLite opens and finds a not-committed rollback journal that looks valid, then it rolls it back?

Right.

> Assuming fsync works on both the main database and the hot journal, then I don't see a way that it is not durable? Because, it has to write and sync the full hot journal, then write to the main database, then zero out the hot journal, sync that, and only then does it atomically return from the commit? (assuming FULL and DELETE)

DELETE mode doesn't truncate or zero the journal; it merely deletes it from the directory. You need to switch to TRUNCATE or PERSIST for that behavior: https://sqlite.org/pragma.html#pragma_journal_mode

I confirmed all of this by attaching gdb to SQLite and setting a breakpoint on unlink. At the time of unlink the journal is still "hot" and usable for rollback: https://news.ycombinator.com/item?id=45069533