Be cautious if you're using large databases on iOS. At least until fairly recently, iOS doesn't page dirty mmaped pages back to disk and after enough churn the app will OOM.

▲

zbentley 4 hours ago | parent [-]

Wow, really?

Then what’s the point of memory mapping in the fist place? Or do they suggest manual flush/sync actions for persistence.

	▲	tynorf 3 hours ago \| parent [-]
		IIRC: it is to leverage the OS page cache rather than having a separate buffer pool in user land. By default lmdb uses normal pwrite/fsync for the write path, but can optionally use a writable mapping and (presumably) msync. However, some people think there are problems with this usage: (pdf warning) https://www.cidrdb.org/cidr2022/papers/p13-crotty.pdf