And then again, for databases trying to rely on mmap might lead you to poorer results - for example trying to do in-place update, ignoring compression, dealing

And then again, for databases trying to rely on mmap might lead you to poorer results - for example trying to do in-place update, ignoring compression, dealing with concurrency, etc. Without mmap, and by using append-only data, no updates on exising ones (except metadata), and the ability to do compression might give you a big edge over just trying to work it out through mmap. Check WiredTiger's articles/videos on how they've found previous mmap approach for mongodb to be much slower (I'm not saying mmap is slower than os calls reads, I'm saying it leads to architectural decisions that might limit you later.) (edit) This actually presents it better than above - https://15721.courses.cs.cmu.edu/spring2019/slides/01-inmemory.pdf https://15721.courses.cs.cmu.edu/spring2019/slides/01-inmemo...