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Home -> Community -> Mailing Lists -> Oracle-L -> RE: CPU WAIT I/O statistic
sar may be installed from the Additional Installation CD of Tru64 Unix . you are correct that does NOT come with the Default installation
-----Original Message-----
Sent: Friday, October 11, 2002 3:19 AM
To: Multiple recipients of list ORACLE-L
Pablo - Well, you've passed beyond my expertise, and I can't really add any more. Someone else may reply that is knowledgeable on these issues. Other than that, you may want to find a list devoted to the operating system you are on. In my admittedly meager experience, this tends to be somewhat vendor-dependent, and depends somewhat on the operating system architecture. For example, Tru64 doesn't even have the sar command or the wait column in processor statistics. You may even want to get your hands on a college textbook that explains operating system design and study the chapter on CPU scheduling. Often we have assumptions about how the CPU scheduler works that are unrealistic.
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-----Original Message-----
Sent: Thursday, October 10, 2002 4:19 PM
To: Multiple recipients of list ORACLE-L
Dennis:
Thanks for answering, what do you mean by, or may be what do you think Gaja means by:
"He points out that the Solaris sar -q command has a "%wio" column, a measure of processes that are currently using the CPU, but are waiting for I/O requests to be serviced and hence are not making prudent use of the CPU"
How can the processes be using the CPIU if they are waiting for some I/O requests?
What I'm trying to say is that that can't consume CPU cicles if they are waiting (SLEEPING).
Why does sar shows that these CPU cicles are used in waiting for I/O? Who's using them?
TIA
Pablo - I posted the following paragraph yesterday:
3) I looked in Oracle Performance Tuning 101 to see
what Gaja has to say.
He points out that the Solaris sar -q command has a
"%wio" column, a measure
of processes that are currently using the CPU, but are
waiting for I/O
requests to be serviced and hence are not making
prudent use of the CPU. He
further says that %sys and %wio should be less than
10-15% and if it is
consistently higher you need to get to the bottom of
it, and usually it is a
application causing the problem. No details on how to
get to the bottom.
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-----Original Message-----
Sent: Thursday, October 10, 2002 3:16 PM
To: Multiple recipients of list ORACLE-L
Hi list
Can anyone explain me what exactly does the WAIT I/O column of the sar -u output mean?
Does it represent the % of CPU used by the kernel processes to perform I/O?
As far as I know the waiting processes do no wait actively when they ask for an I/O. right? The OS uses the SLEEP and WAKEUP primitives.
So, Which process is using this CPU? (The WAIT I/O%)
Or does this WAIT I/O have to be taken as if the CPU were idle?
Please shed some light on this.
Thanks
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Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services ---------------------------------------------------------------------To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). Received on Tue Oct 15 2002 - 02:48:21 CDT
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