RE: multiple databases in a single RAC cluster

From: Bobak, Mark <>
Date: Wed, 12 Nov 2008 01:20:00 -0500
Message-ID: <>

Hi Bob,

I run a RAC configuration with multiple databases.

I have a 3 node cluster of HP DL-585s, each running 4 dual core Opterons, and 64GB RAM. Interconnect is dual bonded Gig-E NICs.

On each node, I'm running 4 database instances, plus an ASM instance.

Specifically, RedHat Linux, RHEL4U6.

CRS is 11g, ASM is 11g, and I have 1 database at 11g ( and 3 databases at 10gR2 (

The RAC has been in place for about 2 years, initially w/ the three 10gR2 databases and no 11g components.

About a year ago, I upgraded CRS and ASM to 11g, and added the 11g database.

It's all quite stable and running well. It really comes down to just a few factors:

1.)  Do you have the CPU capacity?
2.)  Do you have the memory?
3.)  Do you have the interconnect bandwidth?

So, here's the downside:
When the call comes in, and someone says "Hey, the system is slow!" or "My query is hanging!", you've got a lot more work to do. Is the problem systemic? Is it related to just one node, or across the cluster? In my case, there's 12 different database instances to look at. It can be a lot more work, just tracking down the root cause of a performance problem.

But, bottom line, it's not horrendously more complex running a RAC cluster w/ multiple databases than it is to run one database on RAC. Once you have the RAC knowledge and expertise, it's just more of the same. The key is making sure you have enough memory/CPU/interconnect capacity.

Hope that helps,


From: [] On Behalf Of Bob [] Sent: Tuesday, November 11, 2008 11:39 PM Cc: oracle-l
Subject: Re: multiple databases in a single RAC cluster

Thanks Matt, wondering if there are any specific white papers ( I couldn't find any)

Im thinking this would be a very complex configuration ie

asm disk separation - per database -

data guard DR for multiple databases....

the interconnect would really take a beating...probably needing nics for each database...

I mean that sounds like a "very" complex.

The client here is looking to save allot of money by consolidating environments of 15 databases on single servers with active passive veritas clusters - moving them to rac

The strategy is to save money (hardware and support) - I'm just not feeling it...

Im looking for some white papers for this type of configuration, and feedback for costs.

To me rac is excellent for a single database with the need for extremely high level of connections (amazon type, banking, financial), and high availability, but mixing many disparate (1-4 single application) databses into a cluster to save money just dosnt make sense.


Matthew Zito wrote:
> Yes, absolutely, we have one customer who has an 8 node RAC cluster that's running 12 databases, each with between 2 and 8 instances, and a pile of other customers with 2-4 node clusters with multiple databases. I'm sure there's some internal limitations as to the number of services that can be registered in the CRS, but I doubt many people run into it.
> Thanks,
> Matt
> --
> Matthew Zito
> Chief Scientist
> GridApp Systems
> P: 646-452-4090
> -----Original Message-----
> From: on behalf of Bob
> Sent: Tue 11/11/2008 9:12 PM
> To: oracle-l
> Subject: multiple databases in a single RAC cluster
> Hi, As much as Ive been browsing / studying rac... Im looking for a
> definitive answers about how many "databases" can be on one rac cluster.
> Say I want to have 4 independent databases on one cluster, is that
> possible? I understand one can easily have multiple instances pointing
> to a single database (sga, control_file, db_name, spfile, archive_dest,
> etc) but what about several independent databses?
> Any documents referencing this?
> I found this on ask tom... just wanted to confirm with this group,
> probably in a more concise manner.
> So, How many databases (sga, control_file, db_name, spfile,
> archive_dest, etc) can be in a single rac cluster?
> thanks
> Bob
> --


Received on Wed Nov 12 2008 - 00:20:00 CST

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