Re: question about cpu usage

On 10/22/2004 08:41:22 PM, Nelson, Allan wrote:
> Response time for interactive users is non-linear with respect to cpu
> utilization. =20

Of course it's non-linear. If OLTP program is well written, it will mostly=20 utilize I/O - screen, disk and network. Solving a small 100,000x100,000 lin= ear=20
system by using Gauss-Jordan method is seldomly a part of an OLTP program. Also, very few programs are created optimal. If I, for the sake of speed of development write a perl/DBI program that utilizes perl "FORMAT" statement, I'll sacrifice the speed of the program itself. I'll page in the whole perl interpreter, then by executing "use DBI;" I'll load and map an additional d= ynamic=20
library, and I'll do so again when I execute "DBI->connect("dbi:oracle:$db"= ,$usr,$pwd)".
If I start using additional modules like LWP or MIME::Lite it will expand t= hat
perl interpreter to monumental proportions. Address space can easily exceed=  100MB.
The same thing will happen if Java is used. Any other application developme= nt tool=20
like ColdFusion or Oracle*Forms is many times as expensive as perl or Java.=  If=20
your box is running only a single database, the situation is clear but if t= here are
things like LVM, backup server, print spooler or X11, the situation can be = very=20
different. Sendmail with decent rule set, connecting to SpamAssassin and Cl= amAV can
also waste quite a bit of resources, including the CPU, especially if SpamA= ssassin=20
is version 3.0 equipped with all the submodules (Pyzor, DCC, Spamcop). It i= s=20
multithreaded and humongous and can easily waste a whole SMP system. On the=  other=20
hand, if the app system is written by using an efficient TP monitor like Tu= xedo, Top End
or CICS and C/C++, then running out of CPU can mean that you desperately ne= ed a HW=20
upgrade, not just a better system administrator. To summarize, high CPU utilization is frequently a sign of suboptimal compo= nent. If the=20
CPU is spent in the system mode, there is a problem with a driver or kernel=  component,
like excessive paging. If the CPU is spent in user mode, then it is most l= ikely an
application which shouldn't be on an OLTP system in the first place. Genera= l connections
between OLTP user response time and CPU (ab)use are completely irrelevant a= nd make no=20
sense.
--=20
Mladen Gogala
Oracle DBA

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