Re: spin_count and cpu usage

Hi Tim

Thanks very much foor the reply.

Since spin_count is just a numbe rof loops, if we have a faster CPU shouldnt we increase the value? I mean running 2000 loops in a 3GHZ CPU is definitely not the same as running in a 500MHz CPU. In fact i recall, Guy Harrison wrote a latch related paper mentioning that since 2000 for spin_count has been used since Oracle 7, that is 10 - 13 years ago a higher value for modern CPU wouldnt surprise.

Regarding the CPU usage, if with 8 500MHz CPU I consume 30000 seconds CPU in 1 hour, if I replace those with 1GHZ CPU would I reduce my CPU time/usage to half?

TIA Alex

On 9/4/06, Tim Gorman <tim_at_evdbt.com> wrote:
>
> Spin count has little to do with CPU cycles, and everything to do with
> the duration of non-pre-emptive waits on latches (i.e. column SPIN_GETS
> on V$LATCH). It is literally the count in a loop that Oracle spins
> while waiting non-pre-emptively (i.e. without losing the CPU) for a
> latch. Really, really bad feng-shui to mess with spin count.
>
> Oracle cannot record if your CPU is working "efficiently" or not. All
> it can do is report on how much CPU time was consumed. If you do the
> math, 3 million centi-seconds is 30,000 seconds. An hour has 3,600
> seconds, so eight CPUs can use 28,800 seconds in an hour. It pretty
> much adds up to Oracle consuming all the CPU on your server, which is OK
> if it is the only thing on the server. As far as the discrepency
> between 28,800 and 30,000, don't expect too much accuracy from a
> mechanism that is constantly rounding or truncating micro-seconds to the
> nearest centi-second...
>
>
> amonte wrote:
> > Hi
> >
> > I was wondering if anyone know how is spin_count measured? In CPU
> CYCLES?
> >
> > I havea doubt with CPU usage as well, I undersstand that in v$sysstat
> > it is using centiseconds to measure CPU usage. I wonder how can we
> > determine 1 centisecond is equivalent to how many CPU cycles? For
> > example I have a server with 8 PA-RISC 1200 MHz CPU, in 1 hour it
> > reports 3 million centiseconds usage, am I using fully? Basically is
> > how do you know how efficiently is your CPU working from Oracle
> > Statistics.
> >
> > TIA
> >
> > Alex
> >
>
> --
> --
> -Tim Gorman
> consultant - Evergreen Database Technologies, Inc.
>
> website = http://www.evdbt.com
> email = tim_at_evdbt.com
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