The primary benefit of using direct I/O on a unix system is using less
memory. Direct I/O
bypasses buffer cache which is dynamic on the most of modern Unix (and
Unix-like systems,
for Linux fans) systems. If you have never had any problems with memory,
you're unlikely
to see any benefits. You can even notice a slowdown for the jobs that are
mainly read-only
because by using direct I/O, you eliminated the file system prefetch and
caching effects.
If your database has 1,000 online users, you definitely do want direct I/O,
or each and
every process will cache its small part of DB files in both kernel memory
(buffer cache)
and SGA.
--
Mladen Gogala
A & E TV Network
Ext. 1216
> -----Original Message-----
> From: Nuno Souto [mailto:nsouto_at_bizmail.com.au]
> Sent: Tuesday, October 26, 2004 7:18 AM
> To: Oracle-L_at_Freelists. Org (E-mail)
> Subject: Re: Direct I/O, better performance?
>
>
> 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.
--
http://www.freelists.org/webpage/oracle-l
Received on Tue Oct 26 2004 - 10:23:50 CDT
