All, So, I've been doing some reading about this issue, and I think regardless of what other changes we make we should never enable O_DIRECT automatically on Linux, and it was a mistake for us to do so in the first place.
First, in the Linux docs for open(): ========= In summary, O_DIRECT is a potentially powerful tool that should be used with caution. It is recommended that applications treat use of O_DIRECT as a performance option which is disabled by default. ========= Second, Linus has a quote about O_DIRECT that I think should serve as an indicator to us that directIO will never be beneficial-by-default on Linux, and might even someday be desupported: ============ The right way to do it is to just not use O_DIRECT. The whole notion of "direct IO" is totally braindamaged. Just say no. This is your brain: O This is your brain on O_DIRECT: . Any questions? I should have fought back harder. There really is no valid reason for EVER using O_DIRECT. You need a buffer whatever IO you do, and it might as well be the page cache. There are better ways to control the page cache than play games and think that a page cache isn't necessary. So don't use O_DIRECT. Use things like madvise() and posix_fadvise() instead. Linus ============= -- -- Josh Berkus PostgreSQL Experts Inc. http://www.pgexperts.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers