RE: filesystemio_options setting

We ran into a related problem on RHEL 4 and 10.2.0.2.  After changing from 
ASYNCH to SETALL, after some amount of time CTAS statements were dragging along 
at 50 MB/s.  After changing back to ASYNCH the same statements ran at 400 MB/s. 
 Changing back again to SETALL caused those same statements, after running for 
x amount of time, to gradually drop again to 50 MB/s.  

I've never had time to fully investigate this, so I can't say for sure that 
SETALL was the culprit but it sure seemed that way after a few, basic tests.  
This behavior is opposite of what I would have expected, as it seemed that the 
addition of DIRECTIO seemed to slowly fill up something, killing throughput.  
Yet DIRECTIO should be bypassing filesystem cache so it shouldn't be affected 
by any memory-related setting.  Trying to explain this now has me REALLY 
curious as to what was happening.  Great, more work!

Dave
 

___________________________________
Dave Herring, DBA |   A c x i o m  M I C S / C S O
630-944-4762 office | 630-430-5988 wireless | 630-944-4989 fax
________________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of John Smith
Sent: Tuesday, May 13, 2008 10:19 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: filesystemio_options setting

Hi.  We are running oracle 10.2.0.3 on our test evironment in suse 9.   Emc 
symmetrix storage.  I was going over the settings and discovered that 
filesystemio_options was not set (no value given).  I changed it to setall per 
the Oracle documentation for Linux.  Shortly after that, our queries suddenly 
started running longer, and the culprit appears to be disk IO.  

I understood that this setting could not cause a problem, and all the Oracle 
documentation I could find said to set this value to setall in 10.2.0.3.  I 
unset the value and the problem went away. Can someone shed some light on this?
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