We do use mmap, but we do not use memory mapped files. We use mmap to allocate big chunks of memory from the OS, which we later distribute to our custom memory allocators.

It's not a column store. We are thinking about it, maybe some time in the future as we add more analytical feature. It's a row store.

We do write back to dist. We have a transaction log, which we truncate once it grows over a certain threshold, by taking a snapshot.