CPUSPEED

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Roger - 26 Oct 2007 17:04 GMT

I have a question regarding the CPUSPEED on the DBM config.
When I installed the DB2 the CPUSPEED came to be 3.818116e-07 ?
When did a update dbm cgf using CPUSPEED -1. It came up with a
higher number and when I did this again, it again came up with a
different number , it kept changing every time I updated it.
The same did not happen on another server, the number went high and it
stayed the same.

how is the cpuspeed calcuated and why did it change everytime I
changed it.

Thanks

Lawerence

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Serge Rielau - 26 Oct 2007 18:11 GMT

> I have a question regarding the CPUSPEED on the DBM config.
> When I installed the DB2 the CPUSPEED came to be 3.818116e-07 ?
[quoted text clipped - 6 lines]
> how is the cpuspeed calcuated and why did it change everytime I
> changed it.

DB2 actually runs a little benchmark. So if there is another load on the
server then the number could indeed change.

Cheers
Serge

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Serge Rielau
DB2 Solutions Development
IBM Toronto Lab

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Roger - 26 Oct 2007 22:40 GMT

Thanks Serge,
So whats the best way or time to run the the update dbm to pick a good
number so DB2 can use it when creating access plan. Is the best
time, when the system is idle or when the system is averaging or when
the system is busy ?

Lawrence

BTW : I loved your sessions on IOD 2007

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Serge Rielau - 28 Oct 2007 04:04 GMT

> Thanks Serge,
> So whats the best way or time to run the the update dbm to pick a good
> number so DB2 can use it when creating access plan. Is the best
> time, when the system is idle or when the system is averaging or when
> the system is busy ?

Hmm....tricky question.... I would say averaging...But I have no science
to back that up.

> BTW : I loved your sessions on IOD 2007

Tx, and there I was afraid folks would run out once they realize I did
NOT talk about Unicode ;-)

Cheers
Serge

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Serge Rielau
DB2 Solutions Development
IBM Toronto Lab

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Roger - 29 Oct 2007 14:14 GMT

> > Thanks Serge,
> > So whats the best way or time to run the the update dbm to pick a good
[quoted text clipped - 16 lines]
> DB2 Solutions Development
> IBM Toronto Lab

One more question regarding CPUSPEED. Since its millisec/
instruction, which number depicts its a more powerful cpu...higher
number or lower number ? I wish DB2 would get the model number of CPU
and speed at install time or db2 start time rather than calculate
using a bench mark that varies with the load of the system.

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Haider Rizvi - 31 Oct 2007 01:45 GMT

> One more question regarding CPUSPEED. Since its millisec/
> instruction, which number depicts its a more powerful cpu...higher
> number or lower number ?

Lower number is more powerful cpu.

> I wish DB2 would get the model number of
> CPU and speed at install time or db2 start time rather than
> calculate using a bench mark that varies with the load of the
> system.

DB2 will need to keep a pretty exhaustive list of cpus, and their
relative speeds in the engine. Also the underlying requirement to test
on each and every crank of the cpu clock for every cpu supported!
With virtualized cpus coming online now, it will become even more
difficult. IOW, it is not that easy to keep that list up to date.

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Haider

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