Timo Sirainen put forth on 1/16/2011 12:48 PM: > On Sun, 2011-01-16 at 00:05 -0600, Stan Hoeppner wrote: >> Using O_DIRECT with mbox files, the IOPS >> performance can be even greater. However, I don't know if this applies to >> Dovecot because AFAIK MMAP doesn't work well with O_DIRECT... >> ***Hay Timo, does/can Dovecot use Linux O_DIRECT for writing the mail files? > > mmap doesn't matter, because mbox files aren't read with mmap. But I > doubt it's a good idea to use O_DIRECT for mbox files, because even if > it gives higher iops, you're using more iops because you keep re-reading > the same data from disk since it's not cached to memory. > > As for O_DIRECT writes.. I don't know if it's such a good idea either. > If client is connected, it's often going to read the mail soon after it > was written, so it's again a good idea that it stays in cache. > > I once wrote a patch to free message contents from OS cache once the > message was read entirely, because it probably wouldn't be read again. > No one ever reported if it gave any better or worse performance. > http://dovecot.org/patches/1.1/fadvise.diff
I'd gladly test it but I don't have the resources currently, and frankly, at this time, the prerequisite knowledge of building from source. -- Stan
