Re: to enable O_DIRECT within postgresql

Greg: Thank you very much for your insightful comments on the performance of <br />direct io applied to postgres! That
inspiredme a lot.<br /><br />Tom: thank you for the reference to man page!<br /><br /><div class="gmail_quote">On Fri,
Jun18, 2010 at 2:02 AM, Greg Smith <span dir="ltr"><<a
href="mailto:greg@2ndquadrant.com">greg@2ndquadrant.com</a>></span>wrote:<br /><blockquote class="gmail_quote"
style="margin:0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div class="im">Daniel
Ngwrote:<br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204,
204);padding-left: 1ex;"> I am trying to enable the direct IO for the disk-resident<br /> hash partitions of hashjoin
inpostgresql.<br /></blockquote><br /></div> As Tom already mentioned this isn't working because of alignment issues.
 I'mnot sure what you expect to achieve though.  You should be warned that other than the WAL, every experiment I've
everseen that tries to add more direct I/O to the database has failed to improve anything; the result is neither barely
noticeable,or a major performance drop.  This is particularly futile if you're doing your research on Linux/ext3, where
evenif your code works delivers a speed up no one will trust it enough to ever merge and deploy it, due to the
generallypoor quality of that area of the kernel so far.<br /><br /> This particular area is magnetic for drawing
developerattention as it seems like there's a big win just under the surface if things were improved a bit.  There
isn't. On operating systems like Solaris where it's possible to prototype here by use mounting options to silently
covertparts of the database to direct I/O, experiments in that area have all been disappointing.  One of the
presentationsfrom Jignesh Shah at Sun covered his experiments in this area, can't seem to find it at the moment but I
rememberthe results were not positive in any way.<br /><font color="#888888"><br /> -- <br /> Greg Smith  2ndQuadrant
US Baltimore, MD<br /> PostgreSQL Training, Services and Support<br /> greg@2ndQuadrant.com   <a
href="http://www.2ndQuadrant.us"target="_blank">www.2ndQuadrant.us</a><br /><br /></font></blockquote></div><br />