Re: Real World Experience of Oracle RAC and its ability to Scale

Ian Turner wrote:

> Hi,
>
> I'm currently involved in a evaluation of an application that uses of Oracle
> RAC to scale horizontally.
>
> At full production volumes the supplier is recommending a 12-node database
> cluster - using 2CPU commodity servers. Although the transaction rates are
> likely to be low, probably only:
> - 1 update transaction (consisting of perhaps 10 updates/inserts) per
> second.
> - 10 queries/sec
> on average during the day with more queries and less updates overnight .
> Peak volumes are unlikely to be significantly higher.
>
> In the application architecture of the product some application components
> are hosted on the database server. This provides a standard building block
> to scale the application - so the vendor says.
>
> Normally I would expect to separate the application tier from the database
> tier, and believe that a single database server (4CPU's perhaps) would
> easily be able to handle this kind of transaction load. But with this
> shared server the vendor recommends scaling is by adding these combined
> application/database server's into the cluster.
>
> My understanding is that Oracle RAC would typically be deployed with < 5
> nodes. So I'm looking to identify any real world examples of RAC clusters
> and the transaction rates/numbers of nodes.
>
> I would also be interested to know if there are:
> - any recommendations as to the maximum number of nodes in a RAC cluster
> - any RAC design principles that we should ensure the vendor has followed
> - areas we could/should monitor when performing an assessment of the
> application.
> - ways of predicting RAC performance as additional nodes are added (we are
> unlikely to be able to test the application with 12 nodes so will have to
> factor this up from fewer nodes).
>
> Any other comments on the general stability of the Oracle RAC platform in
> real world production environments would also be appreciated.
>
> regards
>
> Ian

Based on what you've written I'd hide my checkbook and find another vendor.

You are incorrect that RAC is typically deployed with less than 5 nodes: I've seen lots of 8+ node clusters. But I don't see based on what you've written that such is required.

I would suggest that you start with 2 x 2CPU nodes and then buy more if required by testing.

More troubling is that this may well be an indication that they are providing rotten software with block contention issues. If you contact me off-line I can put you in touch with a lab that will allow you to pre-test the application on RAC clusters before you buy.

-- 
Daniel A. Morgan
University of Washington
damorgan_at_x.washington.edu
(replace 'x' with 'u' to respond)