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Home -> Community -> Mailing Lists -> Oracle-L -> FW: raw traces - EXEC: c=10,000 e=40
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
Upcoming events:
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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.
> >
> >
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 Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Cary Millsap INET: cary.millsap_at_hotsos.com Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Wed Dec 03 2003 - 11:29:25 CST
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