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RE: Managing CPU_COUNT for micro-partitioning on AIX

From: <>
Date: Tue, 27 Jun 2006 10:21:21 +1000
Message-ID: <>

Oracle will display what the guest OS presents at instance startup.


When you present 1/10th of a CPU to the guest OS I believe you can actually choose how many logical CPUs you want this to present as.


Eg 1/10th physical CPU presented as 2 logical CPUs will report in Oracle as a cpu count of 2.



From: [] On Behalf Of "Jesse, Rich" <>
Sent: Tuesday, 27 June 2006 7:30 AM
To: <>
Subject: Managing CPU_COUNT for micro-partitioning on AIX


Hey all,

As I'm researching what I need to know about AIX for a new 10gR2
install, I'm wondering about _CPU_COUNT. We're buying an IBM 2x2 (two
dual-core CPUs) JS21 blade that will be running IBM's Advanced POWER
Virtualization (APV). APV is a way to virtualize resources -- let's say
"CPUs" -- for multiple OS installations on the same box, with the
ability to prioritize the virtual partitions' CPU usage. APV enables
assigning a dedicated amount of CPU to individual partitions, as well as
a shared amount of CPUs.

The kicker is that APV allows partial-CPU assignments. For three
virtual partitions, "DEV", "BETA", and "PROD", one could assign 0.1
(yes, "one-tenth") CPUs to each of "DEV" and "BETA" and 2.0 CPUs to
"PROD", leaving the remaining 1.8 CPUs free for the shared pool of CPUs,
giving priority to "PROD". So when "PROD" needed CPU, it would take up
to 3.8 CPUs. And if "DEV" or "BETA" needed more CPU and "PROD" wasn't
using it, they could use up to 1.9 CPUs, depending on priority, up to
the full 4.0 CPUs. That's the gist of APV as I understand it. There's
more at if anyone's

ANYWAY, does anyone know how Oracle would or should handle the
_CPU_COUNT and the continuously variable CPU allowance? I still don't
exactly how the APV Hypervisor determines what a tenth of a CPU is, but
I'm thinking that _CPU_COUNT won't take decimals or fractions. I've
found a possible vague reference to this in licensing at
but nothing regarding performance and init.ora parameters.

And, no, I've already refused to put "DEV" and "PROD" on the same box.
I don't care if it's virtual or not. Because no one's ever had an
HBA/SAN/CPU/RAM fail or not failover perfectly...



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Received on Mon Jun 26 2006 - 19:21:21 CDT

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