RE: cpu on AIX

Henry - Here are my reactions, and hopefully someone that knows how to track system CPU usage back to an application will reply. One thought I have is to run each application on a test server and observe the system I/O there. I haven't tried this. Other thoughts:

1. Are interactive users complaining? If they are, then you have a definite problem.
2. In terms of maxing out the CPU, does this situation continue for long periods of time? For example, I have a financial system that is overloaded at the first of the month, but underutilized the rest of the month. But another system simply couldn't process everything they needed each day, so we had to do something. In that case the users ceased running some reports.
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.
4. Maybe you can get some type of O.S. audit that can report what system calls are being made, and that will give you a clue.

Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
Sent: Wednesday, October 09, 2002 1:38 PM To: Multiple recipients of list ORACLE-L

Dennis,
Thanks for the response, and I agree that CPU is there to be used. If you have got it, you might as well use it (0% idle isn't necessarily a bad thing). However, 0% idle could also mean you need more than you've got, and the bottleneck is CPU. (IBM's doc says "typically, the CPU is pacing (the system is CPU bound) if the sum of user and system time exceeds 90% of CPU resource on a single-user system or 80% on a multi-user system. This condition means that the CPU is the limiting factor in system performance").

In this case, multiple applications are running on a single server. Application A is running slowly (wait states don't show any abnormal Oracle contention). The CPU seems to be the bottleneck slowing down the machine. One process running on Application B is using a large chunk of the CPU
(~30%). I think it is using a lot more than this if you take the system io
calls into account. The stronger the evidence, the easier it will be to get Application B to tune/reschedule their process. That is why I am trying to find the system CPU usage initiated by this user process.

Henry

-----Original Message-----
WILLIAMS
Sent: Wednesday, October 09, 2002 1:54 PM To: Multiple recipients of list ORACLE-L

Henry - The issue isn't whether all the CPU is being used, but whether it is being used well. If the O.S. is handling priorities well, servicing your online users crisply, and just giving the excess CPU to a batch-type program, then that is okay. Do you think the O.S. should throw away 10% of the CPU for the heck of it? If users are experiencing sluggish response, then you have a tuning problem to diagnose.

   If you use STATSPACK, take a couple of snapshots and see what the waits are. If not, look at V$SESSION_EVENT.

Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
Sent: Wednesday, October 09, 2002 12:04 PM To: Multiple recipients of list ORACLE-L

I'm working on an AIX (4.3) box which seems to be CPU bound. vmstat and iostat -t both show idle cpu and iowait at 0%. User and system cpu are about 40/60. While trying to track down the source of this load, I looked at the %cpu (-o pcpu) of the processes. One process, spawned from an import, was using about 30% of the cpu. The sum of all pcpu obtained from ps doesn't break 35-40%. I am assuming that this is user cpu, and that the import process is using 3/4 of the user cpu. Since the import is io intensive, I am guessing it is also using a healthy chunk of the system cpu. Is there any way to track this down? Multiple applications (manned by different teams) run on the same server, and so the more I can irrefutably nail down, the better.

Thanks for the help.

Henry

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