Sync notifications need to be async. That goes for `fsync()`/`fdatasync()` as well as for `COMMIT`. In the case of a database-using application you can report

Sync notifications need to be async. That goes for `fsync()`/`fdatasync()` as well as for `COMMIT`. In the case of a database-using application you can report transaction non-failure (as in: it was well-formed and accepted) in a UI separately from transaction durability success (i.e., it really finished), and if you have replication to worry about, you can also report replication success separately. Every blocking operation needs an async variant. Everything should be async-first.