| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
 |
 | |||
| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
|
| |||
Home -> Community -> Mailing Lists -> Oracle-L -> RE: Negative wait time
Yep, right after I wrote my reply, I picked up your book, and started
skimming chapter 7. I quickly realized that I'd oversimplified a
bit....
Mark J. Bobak
Oracle DBA
ProQuest Company
Ann Arbor, MI
"Imagination was given to man to compensate him for what he is not, and
a sense of humor was provided to console him for what he is." --Horace
Walpole
-----Original Message-----
From: Cary Millsap [mailto:cary.millsap_at_hotsos.com]=20
Sent: Monday, February 02, 2004 11:33 AM
To: oracle-l_at_freelists.org
Subject: RE: Negative wait time
Not exactly, but kind of. It's not a negative "wait event" duration, after all; it's that the difference e - c is negative (that is, c > e).
It's possible that some process got a c=3D10000 recorded in its process table when the process spent only, say, 100 microseconds on the CPU. So, for a single dbcall, you really don't have enough data to determine what's going on. But over a span of several dbcalls, your negative and positive quantization errors will tend to offset each other. As long as total "unaccounted-for" time is between -10% and +10% of your total response time, it's safe to ignore it.
By the way, another cause of the c > e phenomenon is the fact that Oracle double-counts some CPU time in both the 'c' and 'ela' statistics. The problem is most prominent for applications that do large multi-block read calls.
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *
Upcoming events:
- Performance Diagnosis 101: 2/24 San Diego, 3/23 Park City, 4/6 Seattle
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Jamadagni, Rajendra
Sent: Monday, February 02, 2004 9:54 AM
To: oracle-l_at_freelists.org
Subject: RE: Negative wait time
Thanks Cary, so is it okay to ignore negative wait times?
Raj
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Cary Millsap
Sent: Monday, February 02, 2004 10:48 AM
To: oracle-l_at_freelists.org
Subject: RE: Negative wait time
Quantization error.
The error is greater on the 'c' statistic than any other, because it is obtained by polling in 10,000-microsecond increments.
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *
Upcoming events:
- Performance Diagnosis 101: 2/24 San Diego, 3/23 Park City, 4/6 Seattle
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Jamadagni, Rajendra
Sent: Monday, February 02, 2004 8:03 AM
To: Oracle List (E-mail)
Subject: Negative wait time
Okay it is Monday and I seem to have difficulty remembering stuff ...
I wrote a pl/sql procedure that analyzes a given trace file and produces
output like this ... but look at wait time ... why is it < 0 ??=3D20
wait =3D3D elapsed-cpu right? What am I missing? In case you are =
wondering
... this procedure (and its output) is based on Cary's paper 'LIO Vs
PIO' ... not precise, but should be pretty close.
SQL Hash Value : 98525727
SELECT count(distinct(us.Ut_Id)) Res_Prmpt
From yyyy ms, zzzz us
Where ms.Mg_Unit_Id =3D3D us.Ut_Id
And us.Pob_Id =3D3D :b4
and ( :b3 IS NULL OR us.Line_Number =3D3D :b3 )
And us.Monday_Dt between :b2 AND :b1
And us.Makegood =3D3D 'A'
And us.Reason_Cd <> -19
And ms.Mg_Unit_Type =3D3D 'P'
And us.Ut_Id Not In (Select ms1.Mg_Unit_Id
From xxxx ms1, yyyy mh
Where ms1.Mg_Number =3D3D mh.Mg_Number
And ms1.Mg_Unit_Type =3D3D 'M'
And mh.Mg_Pob_Id =3D3D :b4
And mh.Mg_Line_Number =3D3D us.Line_Number)
-------- Response Time --------
Action Count Rows Ela Time CPU Time Wait Time LIO Blocks PIO
Blocks
Any pointers are welcome, and yes please excuse me while I go have
another coffee.
Raj
-- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------Received on Mon Feb 02 2004 - 10:52:21 CST
 |
 |