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RE: CPU WAIT I/O statistic

From: Pablo Rodriguez <p_rodri99_at_yahoo.es>
Date: Thu, 10 Oct 2002 13:18:41 -0800
Message-ID: <F001.004E63A4.20021010131841@fatcity.com>


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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Received on Thu Oct 10 2002 - 16:18:41 CDT

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