By default yes, that’s true. But while there isn’t a reliable don’t-flush-this-page system, there definitely are ways to force the flush of specific ranges in an mmapped file.
But you’re generally right. I think that’s why most databases have the notion of a WAL, which is carefully append-only. But the non-WAL data files in most DBs I’ve used are accessed via mmap.
But you’re generally right. I think that’s why most databases have the notion of a WAL, which is carefully append-only. But the non-WAL data files in most DBs I’ve used are accessed via mmap.