Some applications, like Apache Kafka, don't immediately fsync every write. This lets the kernel batch writes and also linearize them, both adding speed. Until synced, the data exists only in the linux page cache.
To deal with the risk of data loss, multiple such servers are used, with the hope that if one server dies before syncing, another server to which the data was replicated, performs an fsync without failure.
I feel like you can try to FAFO with that on a distributed log like Kafka (although also... eww, but also I wonder whether NATS does the same thing or not...)
I would think for something like a database, at most you'd want to have something like the io_uring_prep_fsync others mentioned with flags set to just not update the metadata.
To be clear, in my head I'm envisioning this case to be a WAL type scenario; in my head you can get away with just having a separate thread or threads pulling from WAL and writing to main DB files... but also I've never written a real database so maybe those thoughts are off base.
