On Thu, Jul 13, 2023 at 6:50 AM Dimitrios Apostolou <jimis@gmx.net> wrote:
> Interesting and kind of sad that the last update on the wiki page is from
> 2021. What is the latest prototype? I'm not sure I'm up to the task of
> putting my database to the test. ;-)
It works pretty well, certainly well enough to try out, and work is
happening. I'll try to update the wiki with some more up-to-date
information soon. Basically, compare these two slides (you could also
look at slide 11, which is the most most people are probably
interested in, but then you can't really see what's going on with
system call-level tools):
https://speakerdeck.com/macdice/aio-and-dio-for-postgresql-on-freebsd?slide=7
https://speakerdeck.com/macdice/aio-and-dio-for-postgresql-on-freebsd?slide=9
Not only are the IOs converted into 128KB preadv() calls, they are
issued concurrently and ahead of time while your backend is chewing on
the last lot of pages. So even if your file system completely fails
at prefetching, we'd have a fighting chance at getting closer to
device/line speed. That's basically what you have to do to support
direct I/O, where there is no system-provided prefetching.