Re: Adding CPU to a unix box--added capacity.

If you double number of CPUs then it's likely that your CPU consumption in percentage of total capacity will be halfed providing you keep the same workload and there is no overherad of adding CPU from hardware and OS point of view which is probably fair assumption these days (at least going from 8 to 16 CPUs).

However, increasing workload might (and generaly does for Oracle) cause disproportional growth of CPU consumption and adding 100% of CPU capacity doesn't mean you can process twice as much even if no other bottlenecks are created.

Just my 2 cents.

Alex

On 11/2/07, Zhu,Chao <zhuchao_at_gmail.com> wrote:
> hi,
> Does anyone have experience on adding new CPU to a existing box, like
> upgrade from 8CPU to 16 CPU for example.
> I am curious about two things;
> 1. How many CPU usage% drop do we expect? Like previously it is running at
> 50% CPU usage, typically will it drop to 25%? or something like 30%? To ask
> the same question from another view, is , how much capacity we add to the
> box? 16CPU box = 1.X(?) of a 8CPU box. Assuming same archtecture/OS. (same
> cpu count server in different architecture may have different processing
> power?)
> Would be nice if you can share with your experience (like on
> solaris/aix/hp etc). That's kind of typical server scalability.
>
> 2. Can we say, CPU_USED_BY_THIS_SESSION (stat in oracle) ~~
> Unix_CPU_COUNT * USER_MODE_CPU% (vmstat usr column)? I did couple of compare
> in my database, they look pretty close.
>
> Does anyone ever thinking about have such a formular: it could be very
> fun.
> CPU_USED_BY_THIS_SESSION = X*logical_reads + Y*physical_reads + Z*sorts + A
> * executions + B * redo_size + C * Latch_Spins+ .......?
>
> by the way, anyone like the book"forecasting oracle performance"?
> --
> Regards
> Zhu Chao
> www.cnoug.org
>

-- 
Alex Gorbachev, Oracle DBA Brewer, The Pythian Group
http://www.pythian.com/blogs/author/alex http://www.oracloid.com
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