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Re: Oracle RAC cost justification?

From: Martic Zoran <>
Date: Fri, 3 Jun 2005 00:18:50 -0700 (PDT)
Message-ID: <>

There is not argument about scalability that I know.

Probably there are some applications that will even scale better on RAC somehow (never think that deep, because never need it to) as per some Oracle sales "demo" :)

>From my experience with working on huge Sun and HP platforms (108, 64, 24, ... CPU boxes usually in the cluster because of the customers policy) for "unknown" customers they can scale very well up even up to that number of CPU's dependant what is your application doing of course.

Oracle, itself when hitting the same table may be very unscalable, even doing just lookups (SELECT) on the same table from N processes (N<number of CPU's) is not fully scalable.
We all know why, do not we?

I tested myself in HP labs, certain parts of our application, on the 64-CPU machines and got almost the perfect scalability with 90% user time and 10% system time and 0% I/O.

We tested one big customer end solution, of course just piece using bulk insert into the same partitioned table (up to a billion records per day, as per real production need) having again almost perfect scalability. The instance had 130G SGA.

Some things will scale, some will not.
I do not agree that 108 CPU Sun or 64 CPU HP or whatever machine is not going to scale just because of the number of CPU's. That was maybe true many years ago, I am relatively new in a big HW arena (3 years). It is usually not scaling when you hit some other bottlenecks then the OS and HW, like Oracle critical latches, network, application spin locks, to not mention more obvious stupid things in your app or Oracle because of "nice" design.

I am not going to spend too much words describing the difference in performances while using RAC with two machines with the same number of CPU's as that one big beast.
Just I never got the figures even near these while using RAC with even small number of CPU's in the situations where you load balance the work over two nodes. Of course I am talking about pushing specific Oracle operations to the limit, like inserts.

This does not mean that RAC will not scale while having nicely partitioned application touching different tables and indexes on the different nodes.

The big argument for RAC I know is when you have the system on the HW that cannot be expand. We had the situation where there is no bigger machine on the particular OS market, so to do pure horizontal scaling you can add the node with the RAC or invent somehow horizontal application solution working with many partitioned databases.
We all buy machines for the next 3 years usage. Correct?

RAC is probably very meaningful in Linux and Windows environments as already mentioned where you are limited on specific number of CPU's (It was 8, but probably this expands as IBM, HP and others are in the Linux game for some time).

The ugly thing about this is that your application or third party apps were never designed to work properly in the RAC environment, or even when designed (I tried a few times) could not get the results as one machine.


> But I don't think that there is any
> argument that either SMP or
> NUMA scales much more effectively than RAC/OPS, is
> there?

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Received on Fri Jun 03 2005 - 03:23:46 CDT

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