[hyc_symas]

The loader doesn't perform any sync calls. It really doesn't need to since the DB is larger than RAM - eventually the FS cache fills and then every newly written page will force an existing dirty page to get flushed.

To answer the parent post, when using the raw block device we're actually using mmap already. That's what LMDB means: Lightning Memory-Mapped Database. And while not all raw devices support read/write calls, if they support mmap we use it. But writing thru mmap actually performs poorly for larger-than-RAM DBs. Whenever you access a new page, the OS takes a page fault to page it in from storage first. It's a wasted I/O in this case because we're about to overwrite the entire page.