In regard to conclusion 2, there is another approach here - when you're finished with an old segment, posix_fadvise(..., POSIX_FADV_DONTNEED) can be used to drop it from the page cache.
That would be true if we were using C++. Unfortunately, all our code is in Scala and we use Java NIO libraries to memory map our files. AFAIK, they don't give us the option on using these POSIX calls.
