Re: The ill effects of NOT using direct I/O

Allen, Brandon wrote,on my timestamp of 15/02/2011 8:33 AM:

Yes, Concurrent IO is better than Direct IO on AIX, but there is no need to set 
cio in the mount options anymore either - filesystemio_options=setall will take 
care of it in 10g+:

http://download.oracle.com/docs/cd/B19306_01/server.102/b15658/appa_aix.htm#i631245

"With Oracle Database 10g, you can enable Direct I/O and Concurrent I/O on JFS/JFS2 
at the file level. You can do this by setting the FILESYSTEMIO_OPTIONS parameter in the 
server parameter file to setall or directIO. This enables Concurrent I/O on JFS2 and 
Direct I/O on JFS for all data file I/O. Because the directIO setting disables 
asynchronous I/O it should normally not be used. As a result of this 10g feature, you can 
place data files on the same JFS/JFS2 file system as the Oracle home directory and still 
use Direct I/O or Concurrent I/O for improved performance. As mentioned earlier, you 
should still place Oracle Database logs on a separate JFS2 file system for optimal 
performance."




This must be a doco error.  JFS does not support cio.
As that same link shows in the "File System IO Options", Concurrent IO does not work for jfs: it is exclusive to jfs2. That detail should not be forgotten.
I've made a complete blog post nearly 2 years ago of what's needed in 10gr2 and Aix 5.3 to enable cio and hugepages, it's here: 

http://dbasrus.blogspot.com/2009/06/size-sometimes-does-matter.html
And before I get comments along the lines of "you're wrong", please read ALL of it - including the comments - and verify any subsequent replies are within context. The steps and instructions are correct and verified and working as we speak for the specified releases, as clearly indicated in the text. Yes, I know: it's long and a somewhat complex subject, so one can't just "gloss over it". We haven't had a single race condition in nearly 3 years since, whereas before they were common.
Of course if one is running something outside of the stated conditions, then care should be exercised and more research may be needed (it goes without saying, but it never hurts to re-inforce it). 


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Cheers
Nuno Souto
dbvision@xxxxxxxxxxxx
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