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
>
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