It really depends on where you're storing your DB files. If you're using the /data partition it should Just Work. If you're using external storage, yes, android does a bunch of stupid tricks to implement its secure storage, and that interferes with mmap.

Here's the code that resulted from that Stack Overflow question: https://github.com/LMDB/lmdb/blob/mdb.master/libraries/liblm...

After 36 years of writing code, I have more answers than questions.