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"?

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Regards
Zhu Chao
www.cnoug.org

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http://www.freelists.org/webpage/oracle-l