Re: RAC and scalability

From: DA Morgan <>
Date: Mon, 07 Apr 2008 10:07:09 -0700
Message-ID: <>

Andrea wrote:
> On Apr 7, 3:53 pm, Mark D Powell <> wrote:

>> Andrew, I know nothing about the hardware you listed but if you want
>> useful responses you need to identify the type of application that you
>> will be running: OLTP, DSS, OLAP, etc ... and identify the current
>> user load.  The Oracle version you will be using is also important.
>> For the solution to be RAC it must involve at least two nodes.
>> Also depending on the application design some applications just do not
>> scale well with RAC.  To really run well under RAC the application
>> should have been designed with RAC in mind.

> unfortunately i can't collect informations on current user loads,
> because this is a new project that merge several applications and
> these apps doesn't current using.
> The type of applications will mainly OLTP on 10g rel. of rdbms.
> Sure 4 CPU is better then 2CPU, but what i want to know is if ScaleUp
> is better then ScaleOut (horizontal scaling) in reference to cost of
> the 2 servers describes up.
> So if bl480c server with dual CPU have cost of 6.000$ and bl680c with
> 4 CPU is 12.500$ (double), in RAC environment it is better 2 nodes of
> bl680c or 3-4 nodes of bl480c ?
> thanks again
> Andrew

You are approaching this in a way that may well lead to success or, just as easily, lead to failure. This is not how one approaches RAC design.

The number of CPUs for RAC should be roughly the same number of CPUs for a standalone environment (assume scaling at ~80%). What matters is how the application handles the sharing of blocks between nodes. If there is a lot of sharing RAC is likely not going to scale well no matter the hardware.

 From Oracle's standpoint a 2 node cluster is a special case and you should always try to go with a 3 node minimum.

So, unless you can answer questions about node affinity, my recommendation would be to begin development on a single server, identify CPU requirements, and then add a second server and see how your application scales with cache fusion. To be successful it must understand how RAC works and design services accordingly.

Daniel A. Morgan
Oracle Ace Director & Instructor
University of Washington (replace x with u to respond)
Puget Sound Oracle Users Group
Received on Mon Apr 07 2008 - 12:07:09 CDT

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