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RE: CPU rounding

From: <Joel.Patterson_at_crowley.com>
Date: Fri, 18 Nov 2011 07:09:56 -0500
Message-ID: <C95D75DD2E01DD4D81124D104D317ACA1B8BB6826D_at_JAXMSG01.crowley.com> 





Sorry Gerry, I didn't see your post for some reason.
Yes, both were on same os version of 5.10



Joel Patterson


Database Administrator


904 727-2546


From: Niall Litchfield [mailto:niall.litchfield_at_gmail.com]
Sent: Thursday, November 17, 2011 4:06 PM
To: gerry_at_millerandbowman.com


Cc: Patterson, Joel; oracle-l_at_freelists.org
Subject: Re: CPU rounding



Gerry



As promised I did ask around.. I got the following response which looks pretty accurate to me;



Although Solaris 10 supports CPU timing data in microsecond increments, Oracle does not appear to use this.  Oracle makes calls to the times() function which is based on the old style sampling performed at each tick, normally every 10 milliseconds.  The behavior Gerry is seeing is expected, based on the system calls Oracle is making.  It is possible to modify the systemwide clock tick rate to be faster, however this can have some side-effects.  The following blog sheds some light on the considerations:  http://blogs.oracle.com/jtc/entry/overhead_in_increasing_the_solaris
It would be nice if Oracle changed the system calls they use on Solaris, to retrieve CPU usage.  Unfortunately times() is a standard Unix function while microstate accounting is a Solaris specific implementation.  It may not seem worth the cost for a Solaris specific change like this.
Solaris 10 uses microstate accounting for most statistics reported through prstat, vmstat and other OS utilities.  I recommend using something like "$ prstat -Lma 5" or "$prstat -Lma -p 12345 5" to monitor the OS process of concern.  This will provide very detailed statistics based on CPU state changes, not sampling.  For example:


-bash-3.00$ prstat -Lma -p 24859 5



   PID USERNAME USR SYS TRP TFL DFL LCK SLP LAT VCX ICX SCL SIG PROCESS/LWPID

 24859 oracle   8.6 9.3 0.1 0.0 0.0 0.0  78 3.7  7K  1K 21K   0 oracle/1
 24859 oracle   0.0 0.0 0.0 0.0 0.0 0.0 100 0.0   0   0   0   0 oracle/2
In this example, the process has two lightweight threads so both are displayed.  The columns show various types of CPU usage and idle times.  These various CPU states are all defined in man pages for prstat.
On Thu, Nov 17, 2011 at 8:22 PM, Gerry Miller <gerry_at_millerandbowman.com<mailto:gerry_at_millerandbowman.com>> wrote:



Thanks Joel. Are those databases on the same server, or at least on the same
Solaris version?  It could be either the database release or the OS version
that is at fault.



Joel.Patterson_at_crowley.com<mailto:Joel.Patterson_at_crowley.com>[1] wrote: column value format
999999999999.999999999999 I get 4 zeroes before the decimal on 11.2.0.1
251290000.000000000000 I get 0 zeroes before decimal on 10.2.0.4
56729894.000000000000 Joel Patterson Database Administrator 904 727-2546<tel:904%20727-2546>


-----Original Message----- From: oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org>[2]

[mailto:oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org>[3]] On Behalf Of Gerry Miller Sent:
Thursday, November 17, 2011 4:13 AM To: gerry_at_millerandbowman.com<mailto:gerry_at_millerandbowman.com>[4] Cc:
Oracle-L Group Subject: Re: CPU rounding Hi I hate to bang on about this but
I am no nearer to a solution. We have 3 Solaris 10 boxes running 11.2.0.2
Enterprise Edition and the problem exists on all 3 and I would like to ask
anyone with the same configuration out there to run: SELECT value FROM
v$sess_time_model WHERE stat_name = 'DB CPU'; and tell me if the results are
rounded to centiseconds, that is, all end with 4 zeroes. Thanks Gerry Gerry
Miller wrote: Hi, Can any one help me get to the bottom of this? We have two
Solaris servers one hosting Oracle 10.1 and the other 11.2. The CPU stats on
the 11g box are rounded to centiseconds while on 10g they are
inmicroseconds:Example: In 11g: select value from v$sys_time_model where
stat_name = 'DB CPU'; VALUE ----------- 27089090000 In 10g: select value
fromv$sys_time_model where stat_name = 'DB CPU'; VALUE -------------
1373214613234 It is the same in v$sess_time_model and I suspect it is an OS
setting that isat the root of the issue. Regards Gerry Miller --

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--



Niall Litchfield


Oracle DBA


http://www.orawin.info



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Received on Fri Nov 18 2011 - 06:09:56 CST












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