On Sun, 2013-06-30 at 18:55 -0400, Greg Smith wrote: > This makes platform level testing a lot easier, thanks. Attached is an > updated copy of that program with some error checking. If the files it > creates already existed, the code didn't notice, and a series of write > errors happened. If you set the test up right it's not a problem, but > it's better if a bad setup is caught. I wrapped the whole test with a > shell script, also attached, which insures the right test sequence and > checks.
Thank you. > That's glibc helpfully converting your call to posix_fallocate into > small writes, because the OS doesn't provide a better way in that > kernel. It's not hard to imagine this being slower than what the WAL > code is doing right now. I'm not worried about correctness issues > anymore, but my gut paranoia about this not working as expected on older > systems was justified. Everyone who thought I was just whining owes me > a cookie. So your theory is that it may be slower because there are twice as many syscalls (one per 4K page rather than one per 8K page)? Interesting observation. > This is what I plan to benchmark specifically next. In the interest of keeping this patch moving forward, do you have an estimate for when this testing will be complete? > If the > posix_fallocate approach is actually slower than what's done now when > it's not getting kernel acceleration, which is the case on RHEL5 era > kernels, we might need to make the configure time test more complicated. > Whether posix_fallocate is defined isn't sensitive enough; on Linux it > may be the case that this only is usable when fallocate() is also there. I'd say that if posix_fallocate is slower than the existing code on pretty much any platform, we shouldn't commit the patch at all. I would be quite surprised if that was the case, however. Regards, Jeff Davis -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers