Re: Direct I/O, better performance?

  • From: "Nuno Souto" <nsouto@xxxxxxxxxxxxxx>
  • To: "Oracle-L@Freelists. Org (E-mail)" <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 26 Oct 2004 21:18:24 +1000

Roger, I wouldn't discount direct I/O completely.
Try it on redo log files. 
The other thing you should be aware is that the standard
file system does a lot of work that you have to compensate
for when you start replacing its functionality.  Readahead
on sequential operations is one obvious one.  

When you bypass file systems - or parts of them - then you 
have to be prepared to do some additional changes to the setup of 
both the OS and Oracle to compensate for this.  Once these are 
done, you should see less CPU use from direct I/O (not less I/O!).  
This is because less instructions are executed for each of the 
I/O requests.

Cheers
Nuno Souto
nsouto@xxxxxxxxxxxxxx
----- Original Message ----- 
From: "Roger Xu" <roger_xu@xxxxxxxxxxx>


> First of all, we do not have performance issue. Secondarily,
> I did not gain anything after I switching to Direct I/O.
> 
> All I have is longer statistics gathering, longer datafile
> 
> backup and some longer jobs.
> 
> Anybody in the list see benefits after switching to Direct I/O?
> 

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