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

A while back we doubled the number of cpu's in a system from 2 to 4. I monitored CPU usage at 5 minute intervals for the week before and the week after.  

For the 4cpu week the average CPU usage was: 26.39815

For the 2cpu week the average CPU usage was: 54.78056  

So, CPU usage pretty much halved which was what we expected. However, that doesn't necessarily mean performance will increase by a factor of 2. It depends on the application. In this case the databases on this server were a mix of OLTP and Datamarts. The OLTP databases did see an improvement but the datamarts didn't. The reason is that OLTP transactions are normally short and sweet, so more could be processed at a given time. In the case of the datamart, the refresh job didn't take advantage of multiple cpu's, so it still took the same amount of time to complete.

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Zhu,Chao Sent: Friday, November 02, 2007 10:32 AM To: oracle-l
Subject: Adding CPU to a unix box--added capacity.

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


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