Whenever any maintenance needs server restarts, there’s a list of unsolved bottlenecks or inefficient code that gets touched a lot at that time. I can understand that heating up the server can take lots of time (though lots of low hanging fruits there), but the way actual shutdown is done, even if there’s not much of dirty data to flush, sucks.
See, developers are perfectionists, and their perfectionism also includes the crazy idea that all memory has to be deallocated at server shutdown, as otherwise Valgrind and other tools will complain that someone leaked memory. Developers will write expensive code in shutdown routines that will traverse every memory structure and deallocate/free() it.
Now, guess what would happen if they wouldn’t write all this expensive memory deallocation code.
OS would do it for them, much much much faster, without blocking the shutdown for minutes or using excessive amounts of CPU. \o/