RE: when to use hugepages

I would go further than Riyaj and say there really is no reason not to use hugepages. Even in the hypothetical scenario he described, I'm not sure the situation would be better without hugepages. The real solution there would be to get more memory.... :-)

Also, don't forget to not only set up hugepages (vm.nr_hugepages in /etc/sysctl.conf) but also make sure Oracle can use them (memlock parameter in /etc/security/limits.conf). And, use output from /proc/meminfo to confirm that the hugepages are both being configured and being allocated by Oracle.

Hope that helps,

-Mark

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Mark J. Bobak
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ProQuest...Start here.

-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Riyaj Shamsudeen
Sent: Monday, October 20, 2008 10:45 AM
To: guillermo.bort_at_eds.com
Cc: oracle-l_at_freelists.org
Subject: Re: when to use hugepages

Hi bort

I just resolved a major performance issue using hugepages, at a client
site. IMHO, only reason I can think of, not using hugepages is that you
are really low on free memory & you have other memory hungry
applications in that server and you don\t want to lock SGA in memory.
pagetables size will be a good indicator to show how much memory is wasted.

It is easy to prove your point. In test server, create a condition such
that free memory is depleted. When kscand/kswapd wakes up freeing up
memory, they will page some part of SGA also. Performance issue will be
visible :-). Run a script in the background capturing per minute
execution time.

Then, setup hugepages, create same conditions and see how performance is.

As long as, you make sure that databases is indeed using hugepages, it
is an excellent choice.

Cheers
Riyaj
The Pythian Group
blog: http://orainternals.wordpress.com

Bort, Guillermo wrote:


>

> Hi all,

>

> After the thread about hugepages a while ago I became interested in

> them, and told the SA about them. He said it's viable in most of our

> environments, so it now lies with me to decide where to use hugepages.

> As I have no experience with this, I'd very much appreciate any

> pointers as to how to decide whether to use hugepages or not in a

> given environment. Also, if you know of a way to 'benchmark' de

> performance to have something to show the customer (as the change

> would require some downtime). I think it goes without saying that this

> will be tested in (redundantly enough) testing and QA environments way

> before we even consider trying it in pre-productive and productive

> environmets.

>

> Thanks in advanced

>

> *Guillermo Alan Bort*

>

> DBA / DBA Main Team

>

> *EDS*, an HP company

>


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