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Re: Response time analysis and TKPROF

From: Anjo Kolk <anjo_at_oraperf.com>
Date: Sat, 04 May 2002 16:13:18 -0800
Message-ID: <F001.00458219.20020504161318@fatcity.com>


The way I am reading Gregs questions, he is asking if service time means CPU time (sys + user). And that is correct.
But this is all on the server side, so in Oracle ......

Anjo.

Stephane Faroult wrote:

> Greg Moore wrote:
> >
> > For a single SQL statement, I'd like to determine the response time
> > components.
> >
> > Since TKPROF output provides totals for Elapsed Time and CPU Time, is it
> > correct to say that the "service time" component is total CPU, and the "wait
> > time" component is total Elapsed Time minus total CPU time?
> >
> > Is this formula perfect, a very good and workable approximation, or way off?
> >
>
> Greg,
>
> Sorry for saying so, but I think that you are erring (unless it's
> me). What is for you the 'service'? I presume that it's getting your
> result from Oracle. So your server is Oracle. But your server itself is
> at the mercy of a number of things and can wait for :
> a) CPU,
> b) a latch,
> c) a lock,
> d) I/Os
> and probably many other things ...
>
> Elapsed time minus CPU time is certainly a 'wait time' component, but
> some of this 'wait' can be a perfectly legitimate part of the 'service'
> - such as waiting for a latch or bringing the block into memory.
>
> Queue theory is indeed very interesting, but what do you want to do with
> it? As I see it, the benefit of knowing service time and wait time is to
> say 'well, if I want to ensure that say 90% of my clients do not spend
> more than xxx time units in the system, then I must have that many
> servers'. Great for sizing hardware, but I am afraid that tackling the
> problem as you are trying to do it cannot lead anywhere. You cannot add
> more of the same SQL query, can you? I mean, can you apply queue theory
> when servers are brought in by clients? Or your query is just a part of
> a 'service' as a transactional monitor understands it, which is, to me,
> a bit different.
> My feeling is that it is wrong to see one SQL statement as a service. A
> business process is a service, and you can diminish service time by
> tuning your code - and I am a bit confused about wait times at this
> level.
> The (primitive) way I see elapsed time and CPU time in tkprof output is
> that first elapsed time is how users see it. If the number of logical
> reads is high, I have a problem (either the query is inherently costly,
> either it is poorly written). If I have a high number of logical reads,
> it is somewhat normal to have physical reads as well, and therefore a
> significant difference between elapsed and CPU time(I/O waits). If I
> have no physical I/O and a huge difference between CPU and elapsed time,
> then either I have locking problems or the system is in a sad state. And
> so on. But I find theorizing difficult at this level.
>
> Contradictors welcome :-).
>
> --
> Regards,
>
> Stephane Faroult
> Oriole Software
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Stephane Faroult
> INET: sfaroult_at_oriole.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Anjo Kolk
  INET: anjo_at_oraperf.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
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Received on Sat May 04 2002 - 19:13:18 CDT

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