Pablo - Another idea. Enter "man sar" at your command line. Here is the
paragraph from the Solaris manual. Hope this helps.
-u Report CPU utilization (the default):
%usr, %sys, %wio, %idle
portion of time running in user mode, running in
system mode, idle with some process waiting for
block I/O, and otherwise idle.
In answer to your question, and I'm going beyond my knowledge and more
guessing:
- When a process is ready for more CPU, it is moved on the "run queue".
- When a process has to wait for I/O, it is moved into a "wait queue".
Now, when the CPU is available and the run queue is empty, then that is
counted as "idle" until a process is moved onto the run queue.
Suppose we further divide "idle" between times where maybe no users are
sending work to the system, and times where the users are waiting, but all
the processes are waiting for I/O. We still continue to call the former
"idle", but call the latter "wait I/O". Does this make sense? Maybe my
guessing will irritate one of the experts into replying.
Dennis Williams
DBA
Lifetouch, Inc.
[EMAIL PROTECTED]
-----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.
[EMAIL PROTECTED]
-----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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