RE: Impact of an incorrect CPUSPEEDNW
Date: Fri, 15 Jan 2010 08:59:04 -0600
Message-ID: <C970F08BBE1E164AA8063E01502A71CF0167DFE5_at_WIN02.hotsos.com>
About the CPU Speed, you could export the system stats, recollect the system stats and see if anything changes. If things go bad then it's a quick fix to import that stats back in and be right back to where you were. My personal experience hasn't show that CPU Speed by itself makes much of a difference. I'm sure there are contexts where it will.
CPU Speed is a bit more complex then just getting the count of CPUs. As I understand it, Oracle runs a small routine called which it calls a "standard unit of work", and collects stats on it's run. With these stats Oracle then calculates the CPU speed. Oracle doesn't just ask the CPU's how fast they are. I don't recall where I read this so I can provide a source at the moment. I'll look into this and valid if this is (still) true (which is something I've wanted to do for a while and this gives me an excellent reason to get that done).
Ric Van Dyke
Hotsos Enterprises
Hotsos Symposium
March 7 - 11, 2010
Be there.
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Teehan, Mark
Sent: Thursday, January 14, 2010 11:22 PM
To: oracle-l_at_freelists.org
Subject: Impact of an incorrect CPUSPEEDNW
I am reviewing system statistics for a number of database servers running various 10g releases. Most are using default NoWorkload settings; but I've noticed something odd: some databases have unexpectedly low values for CpuSpeedNw even though they are running on identical servers. This is because they were migrated from older servers and sys stats were not regathered for the new servers.
The database will not automatically recollect system stats unless they are explicitly deleted. This seems an oversight: given that some values like CPU_COUNT are rechecked every time the database starts; I wonder if CpuSpeedNw should also be rechecked automatically. In some cases the numbers are about 30% what they should be; which means that the optimizer calculations are incorrect. I wonder if regathering them - I don't want to do this unless I can confirm that it will make a significant difference - after all the database has been subsequently tuned to run with a lower CpUSpeedNw setting.
Something else that I'm checking- if you do an RMAN clone, or an import FULL=Y, does it pull over the system stats too? I also posted this to forums.oracle.com.
Any ideas?
Mark
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