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FW: raw traces - EXEC: c=10,000 e=40

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Wed, 03 Dec 2003 09:29:25 -0800
Message-ID: <F001.005D88C1.20031203092925@fatcity.com>


Wolfgang,

The OS has always provided microsecond data to the Oracle kernel (see the 'man gettimeofday' and 'man getrusage'). It's only in release 9 that the Oracle kernel stopped truncating the data at the centisecond digit (by doing an integer division of 10000).

Oracle gets elapsed times by comparing pairs of gettimeofday() calls (truss to find out for yourself). The e=40us is actually accurate to within +/-1us (not counting measurement intrusion effect). The c value is potentially way off, as I explained in the other note.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com

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-----Original Message-----
Wolfgang Breitling
Sent: Tuesday, December 02, 2003 3:54 PM To: Multiple recipients of list ORACLE-L

In Oracle 9, Oracle tries to measure times in microseconds (as opposed to
centiseconds pre-9). However, many Systems only slice time far coarser than
that so Oracle has to fake it to some degree and that faking may be different between cpu time and elapsed time. Take your cpu times for example. They are all 10000 microseconds which is exactly 10000/1000000 =
0.01 = 1 centiseconds. That's a bit too much of a coincidence for me. Who
knows where Oracle get the elapsed times from. I wouldn't put too much faith in the accuracy of an purported elapsed time of 40 microseconds. Unless we are getting at least into the milliseconds range I would regard
all elapsed times as rounding errors.

At 02:09 PM 12/2/2003, you wrote:
>Hi!
>
>I haven't read Cary's book yet (although it's already waiting on my
>bookshelf), but I think CPU time c is measured in timeslice steps
(100ms)
>and elapsed time e is taken from system timer or smth like that. Others
will
>know better :)
>
>Tanel.
>
>----- Original Message -----
>To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
>Sent: Tuesday, December 02, 2003 10:49 PM
>
>
> > Reading Cary's book I understand that c and e are
> > measured via different system calls (haven't truss'ed
> > [well tusc'ed] them yet - I am on HP-UX 11.11), but
> > would anybody know what the reasonable upper limit of
> > c-e might be?
> >
> > I am looking at the trace file where c is more than
> > two orders of magnitude greater than e, which make me
> > wonder if I a have some anomaly on my system
> >
> > Some examples:
> >
> > EXEC
> >

#98:c=10000,e=433,p=0,cr=2,cu=2,mis=0,r=1,dep=1,og=4,tim=1777312113968
> >
> > EXEC
> >

#110:c=10000,e=390,p=0,cr=1,cu=3,mis=0,r=1,dep=1,og=4,tim=1777312181650
> >
> > PARSE
> >

#103:c=10000,e=40,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=1777314524922
> >
> > Oracle 9.2.0.4.0 on HP-UX 11.11
> >
> > Thanks,
> > Boris Dali.
> >
> >



> > Post your free ad now! http://personals.yahoo.ca
> > --
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > --
> > Author: Boris Dali
> > INET: boris_dali_at_yahoo.ca
> >
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services
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>Please see the official ORACLE-L FAQ: http://www.orafaq.net
>--
>Author: Tanel Poder
> INET: tanel.poder.003_at_mail.ee
>
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Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Wolfgang Breitling
  INET: breitliw_at_centrexcc.com

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Author: Cary Millsap
  INET: cary.millsap_at_hotsos.com

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Received on Wed Dec 03 2003 - 11:29:25 CST

Original text of this message

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