Hi Abhi,
Although O_DIRECT can be enabled for those OS'es that support it, testing
performed by development has shown no evidence of performance improvements
hosting large databases on any of the OS;es tested on.
If testing on Linux their is a kernel configuration called "swappiness" that
controls how much the kernel favors swap over RAM:
http://www.linuxvox.com/2009/10/what-is-the-linux-kernel-parameter-vm-swappiness/
When hosting large datasets, as you are, it is recommended this parameter be
changed from is default value of 60 to something like 10, which is what we use
on the dbpedia and lod etc services we host, to reduce that amount of swapping
that takes please on the server.
Note:
1. The swappiness setting resides in the file "/proc/sys/vm/swappiness"
2. The command "/sbin/sysctl vm.swappiness" can be used to view its setting
3. The command "/sbin/sysctl -w vm.swappiness=10" can be used to change its
value
4. Adding the "vm.swappiness = 10" to the file "/etc/sysctl.conf" will force
the value to be set at machine boot time.
Let me know if his helps.
Best Regards
Hugh Williams
Professional Services
OpenLink Software
Web: http://www.openlinksw.com
Support: http://support.openlinksw.com
Forums: http://boards.openlinksw.com/support
Twitter: http://twitter.com/OpenLink
On 9 Feb 2011, at 06:18, Abhi wrote:
> Sorry for the delayed response, I am not very clear as to how o_direct works.
> If I am not mistaken, I think it has to do something with OS page caching,
> where virtuoso also caches data and OS also caches data in the form of page
> files and this double caching is avoided with the o_direct parameter. I maybe
> completely wrong here. If I am please correct me.
>
> I want to test the performance benefits of using this parameter as we are
> expecting load sizes of billions of triples in our store. All I know is that
> o_direct param in the ini file enables this and this is OS dependent. But, is
> there any document out there which says which OSes support this parameter and
> are there any changes that needs to be done in Linux kernal(while compiling
> the Kernal or some config file) to enable this? Any document on this(Unix
> related or Virtuosos related) will help me in better understanding what is
> going on behind the scene.
>
> On Sun, Jan 23, 2011 at 7:41 AM, Hugh Williams <hwilli...@openlinksw.com>
> wrote:
> Hi Abhi,
>
> Is this a Unix or Virtuoso question ie do you want to know what OS'es support
> it or on what OS'es Virtuoso supports it ?
>
> Best Regards
> Hugh Williams
> Professional Services
> OpenLink Software
> Web: http://www.openlinksw.com
> Support: http://support.openlinksw.com
> Forums: http://boards.openlinksw.com/support
> Twitter: http://twitter.com/OpenLink
>
> On 21 Jan 2011, at 03:11, Abhi wrote:
>
> > Is there a list of OSes that support the O_DIRECT param or does anybody
> > know how do i find whether a particular OS supports it?
> >
> > --
> > Cheers,
> > Abhi
> > ------------------------------------------------------------------------------
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>
>
>
> --
> Cheers,
> Abhi
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