Questdb's author here. I do share Ayende's sentiment. There are things that the OP paper doesn't mention, which can help mitigate some of the disadvantages:

- single-threaded calls to 'fallocate' will help avoiding sparse files and SIGBUS during memory write - over-allocating, caching memory addresses and minimizing OS calls - transactional safety can be implemented via shared memory model - hugetlb can minimize TLB shootdowns

I personally do not have any regrets using mmap because of all the benefits they provide